Lakhmir Singh Physics Class 10 Solutions Page No:116
Question 42: An electric kettle rated as 1200 W at 220 V and a toaster rated at 1000 W at 220 V are both connected in parallel to a source of 220 V. If the fuse connected to the source blows when the current exceeds 9.0 A, can both appliances be used at the same time ? Illustrate your answer with calculations.
Solution : P1 = 1200W, P2 = 1000W
V = 220V
Fuse rating = 9A
We know, P = VI
Total current required,
I = P/V
If both the appliances are switched on together, the fuse will get burnt. So, both the appliance cannot be used at same time.
Question 43: What is the main difference in the wiring of an electric bulb and a socket for using an electric iron in a domestic electric circuit ? What is the reason for this difference ?
Solution : No earth connection is required for the bulb connection as it does not draw heavy current and we hardly touch it. A socket for using an electric iron has an earth connection because electric iron has a metallic body and draws a large current.
Question 44: (a) Explain why, it is more dangerous to touch the live wire of a mains supply rather than the neutral wire.
(b) Why is it safe for birds to sit on naked power lines fixed atop tall electric poles ?
Solution : (a) It is more dangerous to touch the live wire rather than the neutral wire because live wire has a high potential of 220V, where as neutral wire has zero potential.
(b) Bird’s body is not connected to the earth, so no current flows through its body into the earth. So, it is safe for birds to sit on naked power lines fixed atop tall electric poles.
Question 45: A domestic lighting circuit has a fuse of 5 A. If the mains supply is at 230 V, calculate the maximum number of 36 W tube-lights that can be safely used in this circuit.
Solution : Let the maximum number of tube-lights be y.
Power of y tube-lights, P = 36y
V = 230V, I = 5A
We know that
P = VI
36y = 230 x 5
36y = 1500
y = 31.94
So, number of tube-lights required are 31.