Three similar light bulbs are connected to a constant voltage dc supply as shown in Fig. 7.32. Each bulb operates at normal brightness and the ammeter (of negligible resistance) registers a steady current. The filament of one of the bulbs breaks. What happens to the ammeter reading and to the brightness of the remaining bulbs?
Ammeter reading Bulb brightness
a. increases increases
b. increases unchanged
c. unchanged unchanged
d. decreases unchanged
The circuit shown in Fig. 7.33 contains a battery, a rheostat, and two identical lamps. What will happen to the brightness of the lamps if the resistance of the rheostat is increased?
Lamp P Lamp Q
a. Less bright Brighter
b. Less brighter Less brighter
c. Brighter Less brighter
d. No change Brighter
Two similar headlight lamps are connected in parallel to each other. Together, they consume 48 W from a 6 V battery. What is the resistance of each filament?
(1) 6
(2) 4
(3) 3.0
(4) 1.5
Two electric bulbs, rated for the same voltage, have powers of 200 W and 100 W, respectively. If their resistances are , respectively then :
1.
2.
3.
4.
If the current in an electric bulb decreases by 0.5%, the power in the bulb decreases by approximately :
(1) 1%
(2) 2%
(3) 0.5%
(4) 0.25%
An electric bulb rated for 500 W at 100 V is used in a circuit having a 200 V supply. The resistance R that must be put in series with the bulb, so that the bulb draws 500 W, is :
(1) 18
(2) 20
(3) 40
(4) 700
A wire, when connected to a 220 V mains supply, has power dissipation . Now, the wire is cut into two equal pieces, which are connected in parallel to the same supply. Power dissipation in this case is . Then is :
(1) 1
(2) 4
(3) 2
(4) 3
Three bulbs of 40 W, 60 W, and 100 W are connected in series with a 240 V source. Then,
(1) The potential difference will be the maximum across the 40 W bulb.
(2) The current will be the maximum in 100 W bulb.
(3) The resistance of the 40 W bulb is the minimum.
(4) The current through the 60 W bulb will be 0.1 A.
The resistance of hot tungsten filament is about 10 times the cold resistance. What will be the resistance of 100 W and 200 V lamp when not in use?
(1) 14,000
(2) 400
(3) 40
(4) 4
Two electric bulbs A and B are rated 60 W and 100 W, respectively. If they are connected in parallel to the same source, then,
(1) both the bulbs draw the same current
(2) bulb A draws more current than bulb B
(3) bulb B draws more current than bulb A
(4) currents drawn in the bulbs are in the ratio of their resistances