Page 65 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

Different scales used for measuring temperature are
1 Celsius ° C
2 Fahrenheit ° F

3 Kelvin K
Basic unit of temperature in SI system is Kelvin.
Many physical properties of materials are effected by temperature including the phase (solid, liquid, gaseous),
density, conductivity etc.

Application of heating effect of electric current
In an electric circuit, the unavoidable heating can increase the temperature of the components and also alter their
properties. However, heating effect of electric current has many useful applications. The most common examples
are electric iron, electric toaster, electric oven, electric kettle and electric heater.
Related problem
1)Two heaters H1 and H2 are connected in parallel across the supply voltage V. When the heater H1 generates
250 kcal heat in 20sec and the heater H2 generates 1000kcal in 40 sec. If the resistance of the heater H1 is
10ohm what is the resistance of heater H2? When both heaters are connected in series and voltage V is applied
across them, how much heat will be produced in kcal in 5sec?
v t
2
Heat produced by heater H1 = kcal
R xJ
1
v x20 = 250
2
Jx10
v 2 = 125 kcal -----------------(1)
J
v t
2
Heat produced by heater H2 = kcal
R xJ
2
v x40 = 1000 kcal ----------------- (2)
2
Jx10
250 20 x R
Therefore, = 2
1000 10 x 40

R 2 = 5 ohm
When both heaters are connected in series
v t
= 2 kcal
(R + R ) x J
1
2
125 x 5
= kcal
(10+5)
= 41.666 kcal
Cells and batteries
LAW OF CONSERVATION OF ENERGY
Energy can neither be created nor destroyed but it can transfer from one form to another form
Cell

A cell is an electrochemical device that converts chemical energy into electrical energy
Symbol

52

CITS : Power - Electrician & Wireman - Lesson 13-19