Page 199 - NCERT Science Class 10 English Medium

15. Two lamps, one rated 100 W at 220 V, and the other 60 W at 220 V, are connected
in parallel to electric mains supply. What current is drawn from the line if the supply
voltage is 220 V?
16. Which uses more energy, a 250 W TV set in 1 hr, or a 1200 W toaster in 10 minutes?
17. An electric heater of resistance 44 Ω draws 5 A from the service mains for 2 hours.
Calculate the rate at which heat is developed in the heater.
18. Explain the following.
(a) Why is the tungsten used almost exclusively for filament of electric lamps?
(b) Why are the conductors of electric heating devices, such as bread-toasters
and electric irons, made of an alloy rather than a pure metal?
(c) Why is the series arrangement not used for domestic circuits?
(d) How does the resistance of a wire vary with its area of cross-section?
(e) Why are copper and aluminium wires usually employed for electricity
transmission?

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