Which of the two switches S1 and S2 shown in Fig. 7.31 will produce short circuiting?

(1) S1

(2) S2

(3) Both S1 and S2

(4) Neither S1 nor S2

Subtopic:  Heating Effects of Current |
 69%
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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

Subtopic:  Heating Effects of Current |
From NCERT
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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

Subtopic:  Heating Effects of Current |
From NCERT
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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 Ω

(2) 4 Ω

(3) 3.0 Ω

(4) 1.5 Ω

Subtopic:  Heating Effects of Current |
 81%
From NCERT
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Two electric bulbs, rated for the same voltage, have powers of 200 W and 100 W, respectively. If their resistances are r1 and r2, respectively then :

1. r1=2r2

2. r2=2r1

3. r2=4r1

4. r1=4r2

Subtopic:  Heating Effects of Current |
 87%
From NCERT
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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%

Subtopic:  Heating Effects of Current |
 73%
From NCERT
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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 Ω

(2) 20Ω

(3) 40 Ω

(4) 700 Ω

Subtopic:  Heating Effects of Current |
 77%
From NCERT
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A wire, when connected to a 220 V mains supply, has power dissipation P1. Now, the wire is cut into two equal pieces, which are connected in parallel to the same supply. Power dissipation in this case is P2. Then P2:P1  is :

(1) 1

(2) 4

(3) 2

(4) 3

Subtopic:  Heating Effects of Current |
 66%
From NCERT
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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.

Subtopic:  Heating Effects of Current |
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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 Ω

(2) 400 Ω

(3) 40 Ω

(4) 4 Ω

Subtopic:  Heating Effects of Current |
 52%
From NCERT
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