A rise of temperature 5°C is observed in a conductor by passi

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 Multiple Choice QuestionsMultiple Choice Questions

381.

Two bulbs rated 200 W, 220V and 100 W, 220V, are connected in series, combination is connected to 220 V supply. Power consumed by the circuit is

  • 8O W

  • 67 W

  • 76 W

  • 65 W


382.

In a potentiometer experiment, the balancing with a cell is at 240 cm. On shunting the cell with a resistance of 2 Ω the balancing length becomes 120 cm. The internal resistance of the cell is

  • 0.5 Ω 

  • 1 Ω 

  • 2 Ω 

  • 4 Ω 


383.

The total current supplied to the circuit by the battery is

  • 1 A

  • 2 A

  • 4 A

  • 5 A


384.

The current in a wire varies with time as I = 5t2 + 2t, where I is in ampere and t is in second. The quantity of charge which has to be passed through a cross-section of wire during the times t = 4 s to t = 6 s is

  • 220 C

  • 340 C

  • 273.34 C

  • 280 C


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385.

Three resistances of 2 Ω, 3 Ω and 6 Ω are connected in parallel and the combination is connected in series with 2 V battery having internal resistance of 1 Ω . The current in the battery is

  • 1 A

  • 3 A

  • 2 A

  • 4 A


386.

An electric cable of copper has just one wire of radius 9 mm with resistance 5 Ω . This single copper wire of cable is replaced by 4 different well insulated copper wires each of radius 3 mm. The total resistance of the cable now will be

  • 22.5 Ω

  • 45 Ω

  • 9 Ω

  • 11.25 Ω


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387.

A rise of temperature 5°C is observed in a conductor by passing a current. If the current is doubled the rise in temperature will be

  • 10°C

  • 20°C

  • 5°C

  • 25°C


B.

20°C

Heat produced in a wire of resistance R in time 't' is

              Q = IRt

Also heat required to raise the temperature of a wire by ΔT is

              Q' = msΔT

Here        Q' = Q

⇒        msΔT = IRt

Since, m, S, R and t are constant.

So, ΔT ∝ I2

⇒  T2T1 = I2I12 = 2II2 = 4

∴     ΔT2 = 4 × 5 = 20°C   


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388.

The current density varies with radial distance r as J =ar2 (where, a is a constant) in a  cylindrical wire of radius R. The current passing through the wire between radial distance R4 and R2 is 

  • 20πaR4331

  • 15πaR4512

  • πaR4332

  • 3πaR4864


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389.

A thermister is dipped in a water bath. As the temperature increases the current in the thermistor also increases. This is due to decrease in

  • resistivity

  • conductivity

  • reactance

  • capacitance


390.

In an AC circuit, voltage and current are given by V = 50 sin (lO0 t) V and I = 50 sin 100 t + π3 A. The power dissipiated in the circuit is

  • 125 W

  • 625 W

  • 1250 W

  • 100 W


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