Does the wattage of a resistor factor into the resistance of a resistor?

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Resistors come in a variety of different ratings based on wattage. As a rule, lower wattage resistors are smaller than higher wattage resistors. I understand the wattage determines roughly how much current it can handle before it burns up.



I am a bit confused, however. Shouldn't the area of resistor also determine its conductivity? If you supplied a 1000 watt resistor with 3.3v and 100ma, for instance, would you get the same reading as you would get if you passed the same current through a 1/8 watt resistor? Furthermore, if you do get the same reading, shouldn't the area of the larger resistor affect the resistance? If you get a different reading, shouldn't resistors specify a power range instead just a maximum rating?










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  • Physical size is not the only thing contributing to a resistor's power capacity. Material is crucial. Lower-rated resistors are carbon, and higher-ones are often wire-wound.
    – Reinderien
    2 hours ago










  • The part you see is just the "package". The actual electrical resistance (that one measures with an ohm meter) is created by "stuff" internal to the package. Cut one open and see!
    – mike65535
    1 hour ago










  • Yes, that's true, but there would be no reason to make them larger than they have to be if the resistive material is the same size.
    – user148298
    1 hour ago










  • You would need to make them larger to dissipate a larger amount of heat. A resistor at 1W will need to dissipate a lot less heat than a 100W if ran at full power. Surface area has a lot to due with how much heat you can dissipate.
    – Robert Fay
    1 hour ago














up vote
2
down vote

favorite












Resistors come in a variety of different ratings based on wattage. As a rule, lower wattage resistors are smaller than higher wattage resistors. I understand the wattage determines roughly how much current it can handle before it burns up.



I am a bit confused, however. Shouldn't the area of resistor also determine its conductivity? If you supplied a 1000 watt resistor with 3.3v and 100ma, for instance, would you get the same reading as you would get if you passed the same current through a 1/8 watt resistor? Furthermore, if you do get the same reading, shouldn't the area of the larger resistor affect the resistance? If you get a different reading, shouldn't resistors specify a power range instead just a maximum rating?










share|improve this question























  • Physical size is not the only thing contributing to a resistor's power capacity. Material is crucial. Lower-rated resistors are carbon, and higher-ones are often wire-wound.
    – Reinderien
    2 hours ago










  • The part you see is just the "package". The actual electrical resistance (that one measures with an ohm meter) is created by "stuff" internal to the package. Cut one open and see!
    – mike65535
    1 hour ago










  • Yes, that's true, but there would be no reason to make them larger than they have to be if the resistive material is the same size.
    – user148298
    1 hour ago










  • You would need to make them larger to dissipate a larger amount of heat. A resistor at 1W will need to dissipate a lot less heat than a 100W if ran at full power. Surface area has a lot to due with how much heat you can dissipate.
    – Robert Fay
    1 hour ago












up vote
2
down vote

favorite









up vote
2
down vote

favorite











Resistors come in a variety of different ratings based on wattage. As a rule, lower wattage resistors are smaller than higher wattage resistors. I understand the wattage determines roughly how much current it can handle before it burns up.



I am a bit confused, however. Shouldn't the area of resistor also determine its conductivity? If you supplied a 1000 watt resistor with 3.3v and 100ma, for instance, would you get the same reading as you would get if you passed the same current through a 1/8 watt resistor? Furthermore, if you do get the same reading, shouldn't the area of the larger resistor affect the resistance? If you get a different reading, shouldn't resistors specify a power range instead just a maximum rating?










share|improve this question















Resistors come in a variety of different ratings based on wattage. As a rule, lower wattage resistors are smaller than higher wattage resistors. I understand the wattage determines roughly how much current it can handle before it burns up.



I am a bit confused, however. Shouldn't the area of resistor also determine its conductivity? If you supplied a 1000 watt resistor with 3.3v and 100ma, for instance, would you get the same reading as you would get if you passed the same current through a 1/8 watt resistor? Furthermore, if you do get the same reading, shouldn't the area of the larger resistor affect the resistance? If you get a different reading, shouldn't resistors specify a power range instead just a maximum rating?







power resistors maximum-ratings ratings






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edited 1 hour ago









pipe

9,19731951




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asked 2 hours ago









user148298

4473623




4473623











  • Physical size is not the only thing contributing to a resistor's power capacity. Material is crucial. Lower-rated resistors are carbon, and higher-ones are often wire-wound.
    – Reinderien
    2 hours ago










  • The part you see is just the "package". The actual electrical resistance (that one measures with an ohm meter) is created by "stuff" internal to the package. Cut one open and see!
    – mike65535
    1 hour ago










  • Yes, that's true, but there would be no reason to make them larger than they have to be if the resistive material is the same size.
    – user148298
    1 hour ago










  • You would need to make them larger to dissipate a larger amount of heat. A resistor at 1W will need to dissipate a lot less heat than a 100W if ran at full power. Surface area has a lot to due with how much heat you can dissipate.
    – Robert Fay
    1 hour ago
















  • Physical size is not the only thing contributing to a resistor's power capacity. Material is crucial. Lower-rated resistors are carbon, and higher-ones are often wire-wound.
    – Reinderien
    2 hours ago










  • The part you see is just the "package". The actual electrical resistance (that one measures with an ohm meter) is created by "stuff" internal to the package. Cut one open and see!
    – mike65535
    1 hour ago










  • Yes, that's true, but there would be no reason to make them larger than they have to be if the resistive material is the same size.
    – user148298
    1 hour ago










  • You would need to make them larger to dissipate a larger amount of heat. A resistor at 1W will need to dissipate a lot less heat than a 100W if ran at full power. Surface area has a lot to due with how much heat you can dissipate.
    – Robert Fay
    1 hour ago















Physical size is not the only thing contributing to a resistor's power capacity. Material is crucial. Lower-rated resistors are carbon, and higher-ones are often wire-wound.
– Reinderien
2 hours ago




Physical size is not the only thing contributing to a resistor's power capacity. Material is crucial. Lower-rated resistors are carbon, and higher-ones are often wire-wound.
– Reinderien
2 hours ago












The part you see is just the "package". The actual electrical resistance (that one measures with an ohm meter) is created by "stuff" internal to the package. Cut one open and see!
– mike65535
1 hour ago




The part you see is just the "package". The actual electrical resistance (that one measures with an ohm meter) is created by "stuff" internal to the package. Cut one open and see!
– mike65535
1 hour ago












Yes, that's true, but there would be no reason to make them larger than they have to be if the resistive material is the same size.
– user148298
1 hour ago




Yes, that's true, but there would be no reason to make them larger than they have to be if the resistive material is the same size.
– user148298
1 hour ago












You would need to make them larger to dissipate a larger amount of heat. A resistor at 1W will need to dissipate a lot less heat than a 100W if ran at full power. Surface area has a lot to due with how much heat you can dissipate.
– Robert Fay
1 hour ago




You would need to make them larger to dissipate a larger amount of heat. A resistor at 1W will need to dissipate a lot less heat than a 100W if ran at full power. Surface area has a lot to due with how much heat you can dissipate.
– Robert Fay
1 hour ago










3 Answers
3






active

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up vote
2
down vote













The size or surface area of a resistor is not related to its resistance. It only determines the resistor's power-handling ability.



A 1000 Ohm resistor will measure 1000 Ohms and have the same effect on current in a circuit regardless of its physical size.



Edit: For most resistors, what you see is mostly just a package that protects or covers the actual resistor element. However, the actual resistor element for a high power resistor will be much larger than one for a low power resistor. The resistance is determined by the resistivity and dimensions of the resistor element - a 1000 Ohm 1/4 Watt resistor will be made with a higher resistivity material than a 1000 Ohm 10 Watt resistor.






share|improve this answer






















  • Can you address @Reinderien's comment? Very interesting.
    – user148298
    1 hour ago











  • @user148298 how do you think that the comment and the two answers "mesh"?
    – Solar Mike
    1 hour ago

















up vote
1
down vote













Shouldn't the area of resistor also determine its conductivity?


No. Resistors with the same external dimensions can have different thicknesses, width, or other geometries of different materials inside.



For example, a soda straw and a steel shaft may have the same dimensions, but would have vastly different resistance.






share|improve this answer



























    up vote
    0
    down vote













    enter image description here



    Figure 1. A carbon film resistor. Photo by Shaddack from Wikimedia Commons.



    This photo shows the internal construction of an unpainted carbon film resistor. A spiral cut has been made in the film through to the ceramic former. For a given film resistivity a range of resistance values can be created by varying the pitch and width of the cut in the film. This one is a little suspect as all the heat will be dissipated in the high-resistance section where the spiral is so they are not spreading it evenly across the film. Presumably this is taken care of in the design calculations.




    Shouldn't the area of resistor also determine its conductivity?




    The resistivity and thickness of the uncut material is controllable in manufacture. Then the cutting operation can fine-tune the resistance value.




    If you supplied a 1000 watt resistor with 3.3v and 100ma, for instance, would you get the same reading as you would get if you passed the same current through a 1/8 watt resistor?




    Only if both are $ R = frac VI = frac 3.30.1 = 33 Omega $. The power dissipated in each would be $ P = I^2R = 0.1^2 times 33 = 33 text mW $ so both would be fine.




    Furthermore, if you do get the same reading, shouldn't the area of the larger resistor affect the resistance?






    schematic





    simulate this circuit – Schematic created using CircuitLab



    Figure 2. (a) A small 100 Ω resistor and (b) another one that can handle four times as much power.



    No. This is taken into account in the design. As shown in Figure 2, if we doubled the width of the track (R2 in parallel with R4) we would halve the resistance but if we series connected another pair (R3 and R5) we would be back at 100 Ω. It's just a matter of design.




    If you get a different reading, shouldn't resistors specify a power range instead just a maximum rating?




    Everything sorted?



    Note that the power rating is determined by the maximum temperature the film can handle. This temperature is reached when the energy gain due to electric heating is equal to the energy lost due to cooling by convection, radiation and conduction. The convection and radiation will be determined by the surface area, $ A = pi r^2 l $ where r is the radius and l is the length. Conduction will be determined mostly by the conduction of the leads and the solder pads.



    Videos:




    • Metal film resistors explained complete with computer generated voiceover.


    • Wirewound resistor manufacture.





    share|improve this answer






















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      3 Answers
      3






      active

      oldest

      votes








      3 Answers
      3






      active

      oldest

      votes









      active

      oldest

      votes






      active

      oldest

      votes








      up vote
      2
      down vote













      The size or surface area of a resistor is not related to its resistance. It only determines the resistor's power-handling ability.



      A 1000 Ohm resistor will measure 1000 Ohms and have the same effect on current in a circuit regardless of its physical size.



      Edit: For most resistors, what you see is mostly just a package that protects or covers the actual resistor element. However, the actual resistor element for a high power resistor will be much larger than one for a low power resistor. The resistance is determined by the resistivity and dimensions of the resistor element - a 1000 Ohm 1/4 Watt resistor will be made with a higher resistivity material than a 1000 Ohm 10 Watt resistor.






      share|improve this answer






















      • Can you address @Reinderien's comment? Very interesting.
        – user148298
        1 hour ago











      • @user148298 how do you think that the comment and the two answers "mesh"?
        – Solar Mike
        1 hour ago














      up vote
      2
      down vote













      The size or surface area of a resistor is not related to its resistance. It only determines the resistor's power-handling ability.



      A 1000 Ohm resistor will measure 1000 Ohms and have the same effect on current in a circuit regardless of its physical size.



      Edit: For most resistors, what you see is mostly just a package that protects or covers the actual resistor element. However, the actual resistor element for a high power resistor will be much larger than one for a low power resistor. The resistance is determined by the resistivity and dimensions of the resistor element - a 1000 Ohm 1/4 Watt resistor will be made with a higher resistivity material than a 1000 Ohm 10 Watt resistor.






      share|improve this answer






















      • Can you address @Reinderien's comment? Very interesting.
        – user148298
        1 hour ago











      • @user148298 how do you think that the comment and the two answers "mesh"?
        – Solar Mike
        1 hour ago












      up vote
      2
      down vote










      up vote
      2
      down vote









      The size or surface area of a resistor is not related to its resistance. It only determines the resistor's power-handling ability.



      A 1000 Ohm resistor will measure 1000 Ohms and have the same effect on current in a circuit regardless of its physical size.



      Edit: For most resistors, what you see is mostly just a package that protects or covers the actual resistor element. However, the actual resistor element for a high power resistor will be much larger than one for a low power resistor. The resistance is determined by the resistivity and dimensions of the resistor element - a 1000 Ohm 1/4 Watt resistor will be made with a higher resistivity material than a 1000 Ohm 10 Watt resistor.






      share|improve this answer














      The size or surface area of a resistor is not related to its resistance. It only determines the resistor's power-handling ability.



      A 1000 Ohm resistor will measure 1000 Ohms and have the same effect on current in a circuit regardless of its physical size.



      Edit: For most resistors, what you see is mostly just a package that protects or covers the actual resistor element. However, the actual resistor element for a high power resistor will be much larger than one for a low power resistor. The resistance is determined by the resistivity and dimensions of the resistor element - a 1000 Ohm 1/4 Watt resistor will be made with a higher resistivity material than a 1000 Ohm 10 Watt resistor.







      share|improve this answer














      share|improve this answer



      share|improve this answer








      edited 34 mins ago

























      answered 2 hours ago









      Peter Bennett

      34.6k12661




      34.6k12661











      • Can you address @Reinderien's comment? Very interesting.
        – user148298
        1 hour ago











      • @user148298 how do you think that the comment and the two answers "mesh"?
        – Solar Mike
        1 hour ago
















      • Can you address @Reinderien's comment? Very interesting.
        – user148298
        1 hour ago











      • @user148298 how do you think that the comment and the two answers "mesh"?
        – Solar Mike
        1 hour ago















      Can you address @Reinderien's comment? Very interesting.
      – user148298
      1 hour ago





      Can you address @Reinderien's comment? Very interesting.
      – user148298
      1 hour ago













      @user148298 how do you think that the comment and the two answers "mesh"?
      – Solar Mike
      1 hour ago




      @user148298 how do you think that the comment and the two answers "mesh"?
      – Solar Mike
      1 hour ago












      up vote
      1
      down vote













      Shouldn't the area of resistor also determine its conductivity?


      No. Resistors with the same external dimensions can have different thicknesses, width, or other geometries of different materials inside.



      For example, a soda straw and a steel shaft may have the same dimensions, but would have vastly different resistance.






      share|improve this answer
























        up vote
        1
        down vote













        Shouldn't the area of resistor also determine its conductivity?


        No. Resistors with the same external dimensions can have different thicknesses, width, or other geometries of different materials inside.



        For example, a soda straw and a steel shaft may have the same dimensions, but would have vastly different resistance.






        share|improve this answer






















          up vote
          1
          down vote










          up vote
          1
          down vote









          Shouldn't the area of resistor also determine its conductivity?


          No. Resistors with the same external dimensions can have different thicknesses, width, or other geometries of different materials inside.



          For example, a soda straw and a steel shaft may have the same dimensions, but would have vastly different resistance.






          share|improve this answer












          Shouldn't the area of resistor also determine its conductivity?


          No. Resistors with the same external dimensions can have different thicknesses, width, or other geometries of different materials inside.



          For example, a soda straw and a steel shaft may have the same dimensions, but would have vastly different resistance.







          share|improve this answer












          share|improve this answer



          share|improve this answer










          answered 1 hour ago









          Olin Lathrop

          277k28330778




          277k28330778




















              up vote
              0
              down vote













              enter image description here



              Figure 1. A carbon film resistor. Photo by Shaddack from Wikimedia Commons.



              This photo shows the internal construction of an unpainted carbon film resistor. A spiral cut has been made in the film through to the ceramic former. For a given film resistivity a range of resistance values can be created by varying the pitch and width of the cut in the film. This one is a little suspect as all the heat will be dissipated in the high-resistance section where the spiral is so they are not spreading it evenly across the film. Presumably this is taken care of in the design calculations.




              Shouldn't the area of resistor also determine its conductivity?




              The resistivity and thickness of the uncut material is controllable in manufacture. Then the cutting operation can fine-tune the resistance value.




              If you supplied a 1000 watt resistor with 3.3v and 100ma, for instance, would you get the same reading as you would get if you passed the same current through a 1/8 watt resistor?




              Only if both are $ R = frac VI = frac 3.30.1 = 33 Omega $. The power dissipated in each would be $ P = I^2R = 0.1^2 times 33 = 33 text mW $ so both would be fine.




              Furthermore, if you do get the same reading, shouldn't the area of the larger resistor affect the resistance?






              schematic





              simulate this circuit – Schematic created using CircuitLab



              Figure 2. (a) A small 100 Ω resistor and (b) another one that can handle four times as much power.



              No. This is taken into account in the design. As shown in Figure 2, if we doubled the width of the track (R2 in parallel with R4) we would halve the resistance but if we series connected another pair (R3 and R5) we would be back at 100 Ω. It's just a matter of design.




              If you get a different reading, shouldn't resistors specify a power range instead just a maximum rating?




              Everything sorted?



              Note that the power rating is determined by the maximum temperature the film can handle. This temperature is reached when the energy gain due to electric heating is equal to the energy lost due to cooling by convection, radiation and conduction. The convection and radiation will be determined by the surface area, $ A = pi r^2 l $ where r is the radius and l is the length. Conduction will be determined mostly by the conduction of the leads and the solder pads.



              Videos:




              • Metal film resistors explained complete with computer generated voiceover.


              • Wirewound resistor manufacture.





              share|improve this answer


























                up vote
                0
                down vote













                enter image description here



                Figure 1. A carbon film resistor. Photo by Shaddack from Wikimedia Commons.



                This photo shows the internal construction of an unpainted carbon film resistor. A spiral cut has been made in the film through to the ceramic former. For a given film resistivity a range of resistance values can be created by varying the pitch and width of the cut in the film. This one is a little suspect as all the heat will be dissipated in the high-resistance section where the spiral is so they are not spreading it evenly across the film. Presumably this is taken care of in the design calculations.




                Shouldn't the area of resistor also determine its conductivity?




                The resistivity and thickness of the uncut material is controllable in manufacture. Then the cutting operation can fine-tune the resistance value.




                If you supplied a 1000 watt resistor with 3.3v and 100ma, for instance, would you get the same reading as you would get if you passed the same current through a 1/8 watt resistor?




                Only if both are $ R = frac VI = frac 3.30.1 = 33 Omega $. The power dissipated in each would be $ P = I^2R = 0.1^2 times 33 = 33 text mW $ so both would be fine.




                Furthermore, if you do get the same reading, shouldn't the area of the larger resistor affect the resistance?






                schematic





                simulate this circuit – Schematic created using CircuitLab



                Figure 2. (a) A small 100 Ω resistor and (b) another one that can handle four times as much power.



                No. This is taken into account in the design. As shown in Figure 2, if we doubled the width of the track (R2 in parallel with R4) we would halve the resistance but if we series connected another pair (R3 and R5) we would be back at 100 Ω. It's just a matter of design.




                If you get a different reading, shouldn't resistors specify a power range instead just a maximum rating?




                Everything sorted?



                Note that the power rating is determined by the maximum temperature the film can handle. This temperature is reached when the energy gain due to electric heating is equal to the energy lost due to cooling by convection, radiation and conduction. The convection and radiation will be determined by the surface area, $ A = pi r^2 l $ where r is the radius and l is the length. Conduction will be determined mostly by the conduction of the leads and the solder pads.



                Videos:




                • Metal film resistors explained complete with computer generated voiceover.


                • Wirewound resistor manufacture.





                share|improve this answer
























                  up vote
                  0
                  down vote










                  up vote
                  0
                  down vote









                  enter image description here



                  Figure 1. A carbon film resistor. Photo by Shaddack from Wikimedia Commons.



                  This photo shows the internal construction of an unpainted carbon film resistor. A spiral cut has been made in the film through to the ceramic former. For a given film resistivity a range of resistance values can be created by varying the pitch and width of the cut in the film. This one is a little suspect as all the heat will be dissipated in the high-resistance section where the spiral is so they are not spreading it evenly across the film. Presumably this is taken care of in the design calculations.




                  Shouldn't the area of resistor also determine its conductivity?




                  The resistivity and thickness of the uncut material is controllable in manufacture. Then the cutting operation can fine-tune the resistance value.




                  If you supplied a 1000 watt resistor with 3.3v and 100ma, for instance, would you get the same reading as you would get if you passed the same current through a 1/8 watt resistor?




                  Only if both are $ R = frac VI = frac 3.30.1 = 33 Omega $. The power dissipated in each would be $ P = I^2R = 0.1^2 times 33 = 33 text mW $ so both would be fine.




                  Furthermore, if you do get the same reading, shouldn't the area of the larger resistor affect the resistance?






                  schematic





                  simulate this circuit – Schematic created using CircuitLab



                  Figure 2. (a) A small 100 Ω resistor and (b) another one that can handle four times as much power.



                  No. This is taken into account in the design. As shown in Figure 2, if we doubled the width of the track (R2 in parallel with R4) we would halve the resistance but if we series connected another pair (R3 and R5) we would be back at 100 Ω. It's just a matter of design.




                  If you get a different reading, shouldn't resistors specify a power range instead just a maximum rating?




                  Everything sorted?



                  Note that the power rating is determined by the maximum temperature the film can handle. This temperature is reached when the energy gain due to electric heating is equal to the energy lost due to cooling by convection, radiation and conduction. The convection and radiation will be determined by the surface area, $ A = pi r^2 l $ where r is the radius and l is the length. Conduction will be determined mostly by the conduction of the leads and the solder pads.



                  Videos:




                  • Metal film resistors explained complete with computer generated voiceover.


                  • Wirewound resistor manufacture.





                  share|improve this answer














                  enter image description here



                  Figure 1. A carbon film resistor. Photo by Shaddack from Wikimedia Commons.



                  This photo shows the internal construction of an unpainted carbon film resistor. A spiral cut has been made in the film through to the ceramic former. For a given film resistivity a range of resistance values can be created by varying the pitch and width of the cut in the film. This one is a little suspect as all the heat will be dissipated in the high-resistance section where the spiral is so they are not spreading it evenly across the film. Presumably this is taken care of in the design calculations.




                  Shouldn't the area of resistor also determine its conductivity?




                  The resistivity and thickness of the uncut material is controllable in manufacture. Then the cutting operation can fine-tune the resistance value.




                  If you supplied a 1000 watt resistor with 3.3v and 100ma, for instance, would you get the same reading as you would get if you passed the same current through a 1/8 watt resistor?




                  Only if both are $ R = frac VI = frac 3.30.1 = 33 Omega $. The power dissipated in each would be $ P = I^2R = 0.1^2 times 33 = 33 text mW $ so both would be fine.




                  Furthermore, if you do get the same reading, shouldn't the area of the larger resistor affect the resistance?






                  schematic





                  simulate this circuit – Schematic created using CircuitLab



                  Figure 2. (a) A small 100 Ω resistor and (b) another one that can handle four times as much power.



                  No. This is taken into account in the design. As shown in Figure 2, if we doubled the width of the track (R2 in parallel with R4) we would halve the resistance but if we series connected another pair (R3 and R5) we would be back at 100 Ω. It's just a matter of design.




                  If you get a different reading, shouldn't resistors specify a power range instead just a maximum rating?




                  Everything sorted?



                  Note that the power rating is determined by the maximum temperature the film can handle. This temperature is reached when the energy gain due to electric heating is equal to the energy lost due to cooling by convection, radiation and conduction. The convection and radiation will be determined by the surface area, $ A = pi r^2 l $ where r is the radius and l is the length. Conduction will be determined mostly by the conduction of the leads and the solder pads.



                  Videos:




                  • Metal film resistors explained complete with computer generated voiceover.


                  • Wirewound resistor manufacture.






                  share|improve this answer














                  share|improve this answer



                  share|improve this answer








                  edited 7 mins ago

























                  answered 12 mins ago









                  Transistor

                  74k572161




                  74k572161



























                       

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