# Factors Affecting The Heating Effect Of A Current.

Question: Factors Affecting The Heating Effect Of A Current.

## Introduction

“Electricity can produce for effects:

HEAT: Hairdryers/kettles, LIGHT: light bulbs, SOUND: speakers, MOTION: motors.

All resistors produce heat when a current flows through them. Whenever a current flows through anything with electrical resistance then electrical energy is converted into heat energy. The more current that flows, the more heat is produced. Also, a bigger voltage means more heating, because it pushes more current through. However, the higher you make the resistance, the less heat is produced. This is because a higher resistance means less current will flow, and that reduces the heating. The amount of heat produced can be measured by putting a resistor in a known amount of water or inside a solid block and measuring the increase in temperature.” (Parsons, 2000)

“Current flow is accompanied by the transfer of electrical energy and it is often necessary to know the rate at which a device brings about this transfer. The power of a device is the rate at which it transfers energy. If the p.d. across a device is V and the current through it is I, the electrical energy W transferred from it in time t is     W = ItV

The power P of the device will be     P = W     = ItV

t         t

P = IV

The unit of power is the watt (W) and equals an energy transfer rate of 1 joule per second, i.e. 1W = 1J s-1. In the expression P=IV, P will be in watts if I is in amperes and V in volts. A larger unit is the kilowatt (kW) which equals 1000 watts.

If all the electrical energy is transformed into heat by the device it is called a ‘passive’ resistor and the rate of production of heat will also be called IV. The resistance is R.

P = IV

= V

R                   V²

R

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