### MCQs of Current Electricity

Showing 31 to 40 out of 119 Questions
31.
Potential gradient of potentiometer is obtained at 6 m and 2 m when two cells are joined in series in (i) helping condition (ii) opposing condition respectively. So ratio of emf of cells is _____
 (a) 1 : 1 (b) 1 : 2 (c) 2 : 1 (d) 3 : 1
32.
Unit of potential gradient is _____
 (a) Vm (b) $\frac{\mathrm{V}}{m}$ (c) Vm2 (d) $\frac{\mathrm{V}}{{m}^{2}}$
33.
For two wires of the same material ratio of their mass is 1 : 2 and ratio of their length is 2 : 1. So ratio of their resistances is _____
 (a) 1 : 4 (b) 4 : 1 (c) 1 : 8 (d) 8 : 1
34.
The resistance of copper wire at 0ºC will be four times at _____ ºC temperature (For copper temperature co-efficient of resistance = 4 x 10-3 ºC-1)
 (a) 400ºC (b) 750ºC (c) 500ºC (d) 450ºC
35.
Equivalent resistance of parallel combination of two wires is $\frac{6}{5}$ Ω. If one wire is broken resistance becomes 2Ω so resistance of broken wire = _____ Ω.
 (a) $\frac{3}{5}$ (b) $\frac{6}{5}$ (c) 2 (d) 3
36.
The current through a wire varies with time as I = I0 + αt, where I0 = 10 A and α = 4 As-1. The charge that flows across a cross-section of the wire in first 10 seconds is _____
 (a) 100 C (b) 200 C (c) 300 C (d) 400 C
37.
The current density along the axis of a cylindrical conductor having radius equal to R is given by $\mathrm{J}={\mathrm{J}}_{0}\left(1-\frac{{r}^{2}}{{\mathrm{R}}^{2}}\right)$. The current along the length of the conductor is _____ . The distance from the axis is given by r.
 (a) $\frac{{\mathrm{\pi }}^{2}{\mathrm{J}}^{2}{\mathrm{R}}^{2}}{2}$ (b) $\frac{{\mathrm{\pi J}}_{0}{\mathrm{R}}^{2}}{2}$ (c) $\frac{{\mathrm{J}}_{0}{\mathrm{R}}^{2}}{4}$ (d) $\frac{{\mathrm{J}}_{0}{\mathrm{R}}^{2}}{2\mathrm{\pi }}$
38.
A copper wire is stretched to make it 0.1% longer. The percentage change in its resistance is _____ . [Assume that the volume of the wire remains constant.]
 (a) 0.1 % (b) 0.2 % (c) 0.3 % (d) 0.4 %
39.
The resistance of the platinum wire of a platinum resistance thermometer at the ice-point is 5 Ω and at steam point is 5.23 Ω. When the thermometer is inserted in a hot bath, the resistance of the platinum wire is 5.795 Ω. The temperature of the bath is _____
 (a) 345.65º C (b) 245.65º C (c) 435.65º C (d) Zero
40.
Two materials have the value of α1 and α2 as 6 x 10-4(ºC)-1 and -5 x 10-4(ºC)-1 respectively. The resistivity of the first material ρ20 = 2 x 10-8 Ωm. A new material is made by combining the above two materials. The resistivity does not change with temperature. The resistivity ρ20 of the second material is _____ . Considering the reference temperature as 20ºC assume that the resistivity of the new material is equal to the sum of the resistivity of its component materials.
 (a) 1.2 x 10-8 Ωm (b) 2.4 x 10-8 Ωm (c) 2.4 x 10-7 Ωm (d) 1.2 x 10-7 Ωm
Showing 31 to 40 out of 119 Questions