A 100W lamp bulb and a 4 kW water heater are connected to a 250V supply. Calculate 
(a) the current which flows in each appliance 
(b) the resistance of each appliance when in use.
 

 Ans.[(a)0.4 A, 16 A, (b) 625 Ω, 15.26 Ω]


Data Given:


Power of the Lamp Bulb = P₁ = 100 W

Power of the Heater = P = 4 KW = 4 x 10³ W

Voltage of the power supply= V = 250 volts


To Find:


(a)
Current flowing through Lamp bulb I = ?
Current flowing through Heater I = ?

(b)
Resistance of Lamp bulb R = ?
Resistance of Heater R = ?



Solution:


(a)
To find Current I flowing through the Lamp bulb 
by using formula P = V I

I₁ = PV

by putting values

I₁ = 100W250V

I₁ = 0.4 A---------------Ans. 1(a)

To find Current I₂ flowing through the heater
by using formula P = V I

I = PV

by putting values

I = 410³W250V

I = 0.016 x 10³ W

I = 16 x 10⁻³x 10³ W

I = 16 A -----------------Ans.2(a)


(b)
According to Ohm's Law

V = I R

or

R = VI

To find the resistance of Lamp bulb R 

R₁ = VI

R₁ = 250V0.4A

R₁ = 625 Ω ----------------Ans. 1(b)



To find the resistance of heater = R

R = VI

R = 250V16A

R = 15.625 Ω -----------------Ans. 2(b)

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