Current Electricity (2nd Nov) - Live Session

The temperature (T) dependence of resistivity $(ρ)$ of a semi-conductor is represented by:
(1)

(2)

(3)

(4)

For ensuring dissipation of same energy in all three resistors $(R_{1}, R_{2}, R_{3})$ conducted as shown in figure, their values must be related as

(1) $R_{1} = R_{2} = R_{3}$
(2) $R_{2} = R_{3} a n d R_{1} = 4 R_{2}$
(3) $R_{2} = R_{3} a n d R_{1} = (1 / 4) R_{2}$
(4) $R_{1} = R_{2} + R_{3}$

The voltage of clouds is $4 \times 10^{6}$ volt with respect to round. In a lightening strike lasting 100 m sec, a charge of 4 coulombs is delivered to the ground. The power of lightening strike is:
(1) 160 MW
(2) 80 MW
(3) 20 MW
(4) 500 KW

Faraday law of electrolysis indirectly shows
(1) quantisation of charge
(2) quantisation of angular momentum
(3) quantisation of current
(4) quantisation of viscosity

Two sources of equal emf are connected to an external resistance R. The internal resistance of the two sources are $R_{1} a n d R_{2} (R_{2} > R_{1}) .$ If the potential difference across the source having internal resistance $R_{2}$ is zero, then
(1) $R = R_{2} - R_{1}$
(2) $R = R_{2} \times (R_{1} + R_{2}) / (R_{2} - R_{1})$
(3) $R = R_{1} R_{2} / (R_{2} - R_{1})$
(4) $R = R_{1} R_{2} / (R_{1} - R_{2})$

In the figure shown, the capacity of ht econdenser c is 2 $μ F$ . The current in 2 $Ω$ resistance is

(1) 9A
(2) 0.9 A
(3) $\frac{1}{9} A$
(4) $\frac{1}{0.9} A$

When the key K is passed at t = 0, which of the following statements about the current I in the resistor AB of the given circuit is true?

(1) I = 2 mA at all t
(2) I oscillates between 1 mA and 2 mA
(3) I = 1 mA at all t
(4) At t = 0, I = 2 mA and with time it goes to 1 mA

what is the equivalent resistance across A and B in the figure shown, if R = 3 $Ω$ ?

(1) 9 $Ω$
(2) 12 $Ω$
(3) 15 $Ω$
(4) 8 $Ω$

The resistance between points A and B is:

1. $\left ( \sqrt{3}+1 \right )R$
2. $\left ( \sqrt{3}-1 \right )R$
3. $4R$
4. $\left ( \sqrt{3}+2 \right )R$

10.

A potentiometer is connected between A and B and the balance point is obtained at 203.6 cm. When the end of the potentiometer connected to B is shifted to C, then the balance point is obtained at 24.6 cm. If now the potentiometer be connected between B and C, the balance point will be at

(1) 179.0 cm
(2) 197.2 cm
(3) 212.0 cm
(4) 228.0 cm

11.

Four wires of the same diameter are connected in turn between two points, maintained at a constant potential difference. Their resistivities are; $ρ a n d L$ (wire 1)., 1.2 $ρ$ and 1.2 L (wire 2), 0.9 $ρ$ and 0.9 L (wire 3) and $ρ$ and 1.5 L (wire 4). Rank the wires according to the rates at which energy is dissipated as heat, greatest first
(1) 4 > 3 > 1 > 2
(2) 4 > 2 > 1 > 3
(3) 1 > 2 > 3 > 4
(4) 3 > 1 > 2 > 4

12.

The resistance of a galvanometer is 50 $Ω$ and current required to give full scale deflection is 100 $μ A$ in order to convert it into an ammeter for reading upto 10 A. It is necessary to put an resistance of
(1) $3.5 \times 10^{- 4} Ω$
(2) $10 \times 10^{- 4} Ω$
(3) $2.5 \times 10^{- 4} Ω$
(4) $5 \times 10^{- 4} Ω$

13.

Two resistances equal at $0 °$ C with temperature coefficient of resistance $α_{1} a n d α_{2}$ joined in series act as a single resistance in a circuit. The temperature coefficient of their single resistance will be:
(1) $α_{1} + α_{2}$
(2) $\frac{α_{1} α_{2}}{α_{1} + α_{2}}$
(3) $\frac{α_{1} - α_{2}}{2}$
(4) $\frac{α_{1} + α_{2}}{2}$

14.

When the power delivered by a 100 volt battery is 20 watts the equivalent resistance of the circuit is:
(1) 100 ohms
(2) 500 ohms
(3) 300 ohms
(4) 350 ohms

15.

The electro-chemical equivalent of a substance is numerically equal to the mass of the substance deposited if a current I flows through the electrolyte for 0.25 seconds. The value of I is:
(1) 1 A
(2) 2 A
(3) 3 A
(4) 4 A

16.

Two wires of same metal have the same length but their cross sections are in the ratio 3 : 1. They are joined in series. The resistance of the thicker wire 10 $Ω$ . The total resistance of the combination is
(1) 5/2 $Ω$
(2) 40/3 $Ω$
(3) 40 $Ω$
(4) 100 $Ω$

17.

A constant voltage is applied between the two ends of a uniform metallic wire. Some heat is developed in it. The heat developed is doubled if-
(1) both the length and radius of wire are halved
(2) both length and radius of wire are doubled
(3) the radius of wire is doubled
(4) the length of the wire is doubled

18.

In the circuit shown in figure, the 5 $Ω$ resistance develops 20.00 cal/s due to the current flowing through it. The heat developedin 2 $Ω$ resistance (in cal/s) is

(1) 23.8
(2) 14.2
(3) 11.9
(4) 7.1

19.

For the circuits shown in figures I and II, the voltmeter reading would be

(1) 2 V in circuit I and 0 V in circuit II
(2) 0 V in both circuits
(3) 2 V in both circuits
(4) 0 V in circuit I and 2 V in circuit II

20.

Three copper wires of lengths and cross sectional areas are (l, A), (2l, A/2) and (l/2, 2A). Resistance is minimum in
(1) Wire of cross-secitonal area A/2
(2) wire of cross-sectional area A
(3) wire of cross-sectional area 2A
(4) same in all the three cases

21.

The effective resistance between points P and Q of the electrical circuit shown in the figure is

(1) $\frac{2 R r}{R + r}$
(2) $\frac{8 R (R + r)}{3 R + r}$
(3) 2r + 4R
(4) $\frac{5 R}{2} + 2 r$

22.

Find out the value of current through 2 $Ω$ resistance for the given circuit

(1) zero
(2) 2 A
(3) 5 A
(4) 4 A

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