Current Electricity

A voltmeter of resistance 20000 Ω reads 5 volt. To make it read 20 volt, the extra resistance required is

• 40000 Ω in parallel

• 60000 Ω in parallel

• 60000 Ω in series

• 40000 Ω in series

Ten identical cells each of potential E and internal resistance r are connected in series to form a closed circuit. An ideal voltmeter connected across three cells, will read

• 10 E

• 3 E

• 13 E

• 7 E

A steady current flows in a metallic conductor of non-uniform cross-section. Which of these quantities is constant along the conductor?

• Electric field

• Drift velocity

• Current

• Current density

On increasing the temperature of a conductor, its resistance increases because the

• relaxation time increases

• electron density decreases

• relaxation time decreases

• relaxation time remains constant

What is the equivalent resistance between A and B in given figure?

• 50 Ω

• 25 Ω

• 75 Ω

• 100 Ω

Assertion:  Long distance transmission of a.c. is carried out at extremely high voltages. 

Reason:  Because when the distance is large, voltage has to be large.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

Given that the mobility of electrons in Ge is 0.4 m² V^-1  S^-1 and electronic charge is 1.6 × 10^-19 C. The number of donor atom ( per m³ ) semiconductor of conductivity 500 mho/m is

• 8 × 10²¹

• 8 × 10¹⁵

• 5 × 10²¹

• 8 × 10¹⁶

A circuit consisting of five resistors each of resistance R, forming a Wheatstone bridge. What is the equivalent resistance of the circuit?

• 2R

• R

• 2R/3

• R/2

Assertion:  Total current entering a circuit is equal to leaving the circuit by Kirchhoff's law. 

Reason:  It is based on conservation of energy.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

In the given circuit, the voltage across the load is maintained at 12 V. The current in the zener diode varies from 0-50 mA. What is the maximum wattage of the diode?

• 12 W

• 6 W

• 0.6 W

• 1.2 W