Chapter 14

The resistance of a bulb filament is \(100 \Omega\) at a temperature \(100^{\circ} \mathrm{C}\). If its temperature coefficient of resistance be \(0.005 /{ }^{\circ} \mathrm{C}\), its resistance will become \(200 \Omega\) at a temperature of (A) \(300^{\circ} \mathrm{C}\) (B) \(400^{\circ} \mathrm{C}\) (C) \(500^{\circ} \mathrm{C}\) (D) \(200^{\circ} \mathrm{C}\)c

An electric bulb is rated \(220 \mathrm{~V}-100 \mathrm{~W}\). The power consumed by it when operated on \(110 \mathrm{~V}\) will be (A) \(75 \mathrm{~W}\) (B) \(40 \mathrm{~W}\) (C) \(25 \mathrm{~W}\) (D) \(50 \mathrm{~W}\)

Two sources of equal EMF are connected to an external resistance \(R\). The internal resistances of the two sources are \(R_{1}\) and \(R_{2}\left(R_{2}>R_{1}\right)\). If the potential difference across the source having internal resistance \(R_{2}\) is zero, then (A) \(R=\frac{R_{2} \times\left(R_{1}+R_{2}\right)}{\left(R_{2}-R_{1}\right)}\) (B) \(R=R_{2}-R_{1}\) (C) \(R=\frac{R_{1} R_{2}}{\left(R_{1}+R_{2}\right)}\) (D) \(R=\frac{R_{1} R_{2}}{\left(R_{2}-R_{1}\right)}\)

An energy source will supply a constant current into the load, if its internal resistance is (A) Equal to the resistance of the load. (B) Very large as compared to the load resistance. (C) Zero. (D) Non-zero but less than the resistance of the load.

In a potentiometer experiment, the balancing with a cell is at length \(240 \mathrm{~cm}\). On shunting the cell with a resistance of \(2 \Omega\), the balancing length becomes 120 \(\mathrm{cm} .\) The internal resistance of the cell is (A) \(1 \Omega\) (B) \(0.5 \Omega\) (C) \(4 \Omega\) (D) \(2 \Omega\)

The resistance of the series combination of two resistances is \(S .\) When they are joined in parallel, the total resistance is \(P .\) If \(S=n P\), then the minimum possible value of \(n\) is (A) 4 (B) 3 (C) 2 (D) 1

An electric current is passed through a circuit containing two wires of the same material, connected in parallel. If the lengths and radii of the wires are in the ratio of \(4 / 3\) and \(2 / 3\), then the ratio of the currents passing through the wire will be (A) 3 (B) \(1 / 3\) (C) \(\underline{8 / 9}\) (D) 2

In a metre bridge experiment, null point is obtained at \(20 \mathrm{~cm}\) from one end of the wire when resistance \(X\) is balanced against another resistance \(Y\). If \(X

A wire when connected to \(220 \mathrm{~V}\) mains supply has power dissipation \(P_{1}\). Now the wire is cut into two equal pieces which are connected in parallel to the same supply. Power dissipation in this case is \(P_{2}\). Then \(P_{2}: P_{1}\) is (A) 1 (B) 4 (C) 2 (D) 3

The supply voltage to a room is \(120 \mathrm{~V}\). The resistance of the lead wires is \(6 \Omega .\) A \(60 \mathrm{~W}\) bulb is already switched on. What is the decrease of voltage across the bulb, when a \(240 \mathrm{~W}\) heater is switched on in parallel to the bulb? (A) \(2.9 \mathrm{~V}\) (B) \(13.3 \mathrm{~V}\) (C) \(10.04 \mathrm{~V}\) (D) Zero V

This question has statement I and statement II. Of the four choices given after the statements, choose the one that best describes the two statements. Statement-I: Higher the range, greater is the resistance of ammeter. Statement-II: To increase the range of ammeter, additional shunt needs to be used across it. (A) Statement-I is true, Statement-II is true, Statement-II is not the correct explanation of Statement-I. (B) Statement-I is true, Statement-II is false. (C) Statement-I is false, Statement-II is true. (D) Statement-I is true, Statement-II is true, Statement-II is correct explanation of Statement-I.

Two electric bulbs marked \(25 \mathrm{~W}-220 \mathrm{~V}\) and \(100 \mathrm{~W}-220\) \(\mathrm{V}\) are connected in series to a \(440 \mathrm{~V}\) supply. Which of the bulbs will fuse? (A) Both (B) \(100 \mathrm{~W}\) (C) \(25 \mathrm{~W}\) (D) Neither

Resistance of a given wire is obtained by measuring the current flowing in it and the voltage difference applied across it. If the percentage errors in the measurement of the current and the voltage difference are \(3 \%\) each, then error in the value of resistance of the wire is (A) \(6 \%\) (B) Zero (C) \(1 \%\) (D) \(3 \%\)

In a large building, there are fifteen bulbs of \(40 \mathrm{~W}\), five bulbs of \(100 \mathrm{~W}\), five fans of \(80 \mathrm{~W}\) and one heater of \(1 \mathrm{~kW}\). The voltage of the electric mains is \(220 \mathrm{~V}\). The minimum capacity of the main fuse of the building will be (A) \(8 \mathrm{~A}\) (B) \(10 \mathrm{~A}\) (C) \(12 \mathrm{~A}\) (D) \(14 \mathrm{~A}\)

In the circuit shown, the current in the resistor is (A) \(0 \mathrm{~A}\) (B) \(0.13 \mathrm{~A}\), from \(Q\) to \(P\) (C) \(0.13 \mathrm{~A}\), from \(P\) to \(Q\) (D) \(1.3 \mathrm{~A}\), from \(P\) to \(Q\)

When \(5 \mathrm{~V}\) potential difference is applied across a wire of length \(0.1 \mathrm{~m}\), the drift speed of electrons is \(2.5 \times\) \(10^{-4} \mathrm{~ms}^{-1}\). If the electron density in the wire is \(8 \times\) \(10^{28} \mathrm{~m}^{-3}\), the resistivity of the material is close to (A) \(1.6 \times 10^{-7} \Omega \mathrm{m}\) (B) \(1.6 \times 10^{-6} \Omega \mathrm{m}\) (C) \(1.6 \times 10^{-5} \Omega \mathrm{m}\) (D) \(1.6 \times 10^{-8} \Omega \mathrm{m}\)

A galvanometer having a coil resistance of \(100 \Omega\) gives a full scale deflection, when a current of \(1 \mathrm{~mA}\) is passed through it. The value of the resistance, which can convert this galvanometer into ammeter giving a full scale deflection for a current of \(10 \mathrm{~A}\), is (A) \(2 \Omega\) (B) \(0.1 \Omega\) (C) \(3 \Omega\) (D) \(0.01 \Omega\)

The temperature dependence of resistances of \(\mathrm{Cu}\) and Si (not doped) in the temperature range \(300-400 \mathrm{~K}\), is best described by (A) linear increase for Cu, exponential increase for Si. (B) linear increase for Cu, exponential decrease for Si. (C) linear decrease for Cu, linear decrease for Si. (D) linear increase for Cu, linear increase of Si.