# Power

## Trending Questions

**Q.**If the voltage across a bulb rated 220 V−100 W drops by 2.5% of its rated value, the percentage of the rated value by which the power would decrease is

- 20%
- 2.5%
- 5%
- 10%

**Q.**The value of power dissipated across the Zener diode (Vz=15 V) connected in the circuit as shown in the figure is x×10−1 watts.

The value of x to the nearest integer is

**Q.**When a 24 V battery is connected to a resistor, the current in it is 0.4 A. What will be the current through it when it is connected to a battery of 6 V ?

- 0.4 A
- 0.1 A
- 0.2 A
- 0.3 A

**Q.**The switch S has been closed for a long time and the electric circuit shown carries a steady current. Let C1=3.0 μF, C2=6.0 μF, R1=4.0 Ω and R2=7.0 Ω. The power dissipated in R2 is 2.8 kW. Then:

- The power dissipated in the resistor R1 is 1.6 kW.
- The charge on capacitor C1 is 240 μC.
- The charge on capacitor C2 is 440 μC.
- When the switch is opened after long time, the charge on C1 is 660 μC.

**Q.**

One Dioptre is equal to ____________

**Q.**If the length of the filament of a heater is reduced by 10%, the power of the heater will

- increase by about 9%
- increase by about 11%
- increase by about 19%
- decrease by about 10%

**Q.**A zener diode having zener voltage 8 V and power dissipation rating of 0.5 W is connected across a potential divider arranged with maximum potential drop across zener diode is as shown in the diagram. The value of protective resistance Rp is ______Ω.

**Q.**12.Two resistance 2 and 4 ohm are connected in series in an electric circuit. Ratio of thermal power dissipated in each resistance is

**Q.**Two zener diodes (A and B) having breakdown voltages of 6 V and 4 V respectively are connected as shown in the circuit below. The output voltage V0 variation with input voltage linearly increasing with time, is given by:

(Vinput=0 V at t=0)

(figures are qualitative)

**Q.**ten 60W, 220 V bulbs are connected in series to220V supply power consumed in circuit i

**Q.**15.Power Dissipated in an LCR series circuit connected to an a.c. source of emf E is ?

**Q.**A series LCR circuit of R=5 Ω, L=20 mH and C=0.5 μF is connected across an AC supply of 250 V, having variable frequency. The power dissipated at resonance condition is _____ ×102 W.

**Q.**An electric bulb, rated as 200 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 delivers the same power is

**Q.**Photodiode can be used as -

- Switch
- Anode
- Photodetector
- Cathode

**Q.**A battery is charged at a potential of 15 V for 8 h when the current flowing is 10 A. The battery on discharge supplies a current of 5 A for 15 h. The mean terminal voltage during discharge is 14 V. The watt-hour efficiency of the battery is

- 80%
- 82.5%
- 90%
- 87.5%

**Q.**A, B, C are identical bulbs. How does the brightness of A and B change when the switch S is closed ?

- The brightness of A increases and that of B decreases.
- The brightness of A does not change and that of B decreases.
- The brightness of both A and B decreases.
- The brightness of A increases and that of B does not change.

**Q.**An electrical bulb rated 220 V, 100 W, is connected in series with another bulb rated 220 V, 60 W. If the voltage across combination is 220 V, the power

consumed by the 100 W bulb will be about ____

**Q.**Prove that in series combination of electric appliances, the reciprocal of total power consumption is equal to the sum of the reciprocals of the powers of individual appliances

**Q.**

L, C and R represent the physical quantities inductance, capacitance and resistance respectively. Which of the following combinations have dimensions of frequency?

1RC

RL

1√LC

CL

**Q.**For the given circuit, the average power developed is -

- 50√2 W
- 200 W
- 50√2 W
- 200√2 W

**Q.**Two thin lenses of focal length f1=10 cm and f2=20 cm are kept as shown. The resultant power of combination will be

- −10 D
- 0
- 10 D
- 5 D

**Q.**Two insulated metallic spheres of \(3 \mu F\) and \(5 \mu F\) capacitance are charged to \(300 V\) and \(500 V\) respectively. The energy loss, when they are connected by a wire is

**Q.**A convergent lens of power 16 D is used as a simple microscope. The magnification produced by this lens, when the final image is formed at least distance of distinct vision is

- 4
- 5
- 6
- 7

**Q.**An engine develops 20 kW of power. How much time will it take to slowly lift a mass of 100 kg to a height of 20 m?

(g=10 m/s2)

- 4 s
- 5 s
- 1 s
- 10 s

**Q.**A thin symmetrical double convex lens of power P is cut into three parts, as shown in the figure. Power of A is:

- 2P
- P2
- P3
- P

**Q.**Four identical bulbs each rated 100 watt , 220 volts are connected across a battery as shown. The total electric power consumed by the bulbs (in watt) is:

**Q.**A man carrying a bag of mass 25 kg climbs up to a height of 10 m in 50 s. The power delivered by him to the bag is

[ Take g=9.8 m/s2 ]

- 64 W
- 36 W
- 49 W
- 23 W

**Q.**N-m/sec is unit of ? a.work b.pressure c.power d.energy

**Q.**The circuit shown below contains two ideal diodes, each with a forward resistance of 50 Ω. If the battery voltage is 6 V, the current through the 100 Ω resistance (in Amperes) is :

- 0.027
- 0.030
- 0.020
- 0.036

**Q.**A condenser of capacity C1 is charged to a potential V0. The electrostatic energy stored in it is U0. It is connected to another uncharged condenser of capacity C2 in parallel. The energy dissipated in the process is

- C1C1+C2U0
- C2C1+C2U0
- (C1−C2C1+C2)U0
- C1C22(C1+C2)U0