• Wire : nichrome 80:20
  • Ohms per metre : 750 ohms per metre
  • Resistance value : 5k ohms
  • Resistors dimensions : 8mm diameter and 50mm.

Voltage I am going to pass is 240v.

How much heat does Resistors dessipate ? (Can I guess the temperature or do we have formula for calculating heat in temperature)

  • \$\begingroup\$ heat in measured in joules, temperature is measured in kelvin (or some lesser units) heat is not measured in temperature. \$\endgroup\$ Commented Nov 4, 2017 at 9:05
  • \$\begingroup\$ Hi jasen so as per information given above can we derive how much heat the Resistors will dessipate in joules \$\endgroup\$ Commented Nov 4, 2017 at 9:07
  • 1
    \$\begingroup\$ 240^2/5k is about 12 watts. In a resistor 50mm long and 8mm diameter in free air, I would guess it will get too hot to touch (>60C), but not hot enough to desolder itself (<180C). I'd be interested to know what temperature you measure when you do the experiment. \$\endgroup\$
    – Neil_UK
    Commented Nov 4, 2017 at 9:41
  • 1
    \$\begingroup\$ Joules is simply power * time. To calculate the temperature you'd need to know the rate of cooling which is highly dependent on the resistor's shape and surface area, and its cooling (particularly the airflow around it). That's a complex problem, much easier to measure. \$\endgroup\$
    – user16324
    Commented Nov 4, 2017 at 9:44
  • \$\begingroup\$ Hi Neil, after doing experiment I am getting temperature of 80 degree centigrade \$\endgroup\$ Commented Nov 5, 2017 at 4:20

1 Answer 1


Reisitance value: 5k ohms.

Voltage I am going to pass is 240 V.

You are not going to "pass" voltage. You will apply the voltage to your load. The result will be that current will pass through the load.

How much heat does resistors dissipate?

The heat will be the electrical power (in watts) consumed by the resistor.

$$ P = VI = I^2R = \frac {V_2}{R} $$

Since you know V and R you can use the last option, \$ P = \frac {V_2}{R} \$.

Can I guess the temperature or do we have formula for calculating heat in temperature.

The temperature will stabilise at the point where heat losses to the environment or the matter you are heating equals the power input. You will probably have to experiment to find the resultant temperature.

The energy you put into the system will be \$ E = P \cdot t \$ and will be in joules (J) or watt-hours (Wh).

  • \$\begingroup\$ Yes.. that's the only option I m doing right now.. \$\endgroup\$ Commented Nov 4, 2017 at 9:29
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    \$\begingroup\$ @MilanUmeshDave you show thanks and appreciation by accepting (ticking) the answer and voting up. Given the quality and effort put into this answer it needs it... \$\endgroup\$
    – Solar Mike
    Commented Nov 4, 2017 at 10:08

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