Class 8 Physics – Electricity Numericals with Solutions

Title: Class 8 Physics Electricity

Question 1

An electrical appliance is rated as 60 W – 150 V.
(a) What do you understand by this statement?
(b) How much current will flow through the appliance when in use?

Solution

(a) Meaning of the statement
150 V is the voltage required to operate the appliance.
60 W is the power consumed by the appliance during operation.

(b) Current flowing through the appliance

Given:
P = 60 W
V = 150 V
Formula:
P=V×I
Rearranging:
I=P/V
Substitution:
I =
I = 0.4 A

Final Answer:
(a) 150 V is the voltage required to operate the appliance and 60 W is the power
consumed during operation.
(b) Current flowing through the appliance = 0.4 A

Question 2

An electric iron of power 1.5 kW is used for 30 minutes to press cloth. Calculate the
electrical energy consumed in
(A) kilowatt hour
(B) joule

, Solution

Given:
Power P = 1.5 kW
Time t = 30 minutes

Convert time into hours:
t =
t = 0.5 hour

(A) Electrical energy in kWh
Electrical energy consumed = Power × Time (in hours)

Step 1: Formula
E=P×t

Step 2: Substitute values
E = (1.5 kW) × (0.5 h)
E = 0.75 kWh

(B) Electrical energy in Joule

Step 1:Convert power
1 kW = 1000 W
P = 1.5 × 1000
P = 1500 W
Convert minutes to seconds
We know:
1 minute = 60 seconds
So,
t = 30 minutes
t = 30 × 60 seconds
t = 1800 seconds
Formula:
E=P×t
Substitution:
E = 1500 × 1800
E = 2,700,000 J
Scientific notation:
E = 2.7 × 10⁶ J