A wire of length Lis drawn such that its diameter is reduced to half of its original diameter. If the initial resistance of the wire were 10 Ω, its new resistance would be

• 40 Ω

• 80 Ω

• 120 Ω

• 160 Ω

An electric dipole placed in a non-uniform electric field experiences

• both a torque and a net force

• only a force but no torque

• only a torque but no net force

• no torque and no net force

23.

If an ideal parallel LC circuit, the capacitor is changed by connecting it to a d.c source which is then disconnected. The current in the circuit 

• becomes zero instantaneously

• grows monotonically

• decays monotonically

• oscillates instantaneously

Three charges are placed at the vertices of an equilateral triangle of side a as shown in the given figure. The force experienced by the charge placed at the vertex A in a direction normal to BC is

• Q² / 4πε₀a²

• - Q^{2 (4πε₀a2<)}

• zero

• Q² / 2πε₀a²

A capacitor of capacitance  2μF is connected in the tank circuit of an oscillator oscillating with a frequency of 1 kHz. If the current flowing in the circuit is 2 mA, the voltage across the capacitor will be

• 0.16 V

• 0.32 V

• 79.5 V

• 159 V

The earth's magnetic field at a  given point is 0.5 × 10^-5 Wb/m². This field is to be annulled by magnetic induction at the centre of a circular conducting loop of radius 5.0 cm. The current required to be flown in the loop nearly

• 0.2 A

• 0.4 A

• 4 A

• 40 A

A frog can be levitated in a magnetic field produced by a current in a vertical solenoid placed below the frog. This is possible because the body of the frog behaves as 

• paramagnetic

• diamagnetic

• ferromagnetic

• antiferromagnetic

Figure shown is a distribution of charges. The flux of electric field due to these charges through the surface S is

• $\frac{3\mathrm{q}}{{\mathrm{\epsilon }}_{\mathrm{o}}}$

• $\frac{2\mathrm{q}}{{\mathrm{\epsilon }}_{\mathrm{o}}}$

• $\frac{\mathrm{q}}{{\mathrm{\epsilon }}_{\mathrm{o}}}$

• zero

An electron is travelling along the x-direction. It encounters a magnetic field in the y-direction. Its subsequent motion will be

• straight line along the x-direction

• a circle in the xz plane

• a circle in the yz plane

• a circle in the xy plane

The difference in lengths of a mean solar day and a sideral day is about 

• 1 min

• 4 min

• 15 min

• 56 min