A conducting circular loop is placed in a uniform magnetic field, B = 0.025 T with its plane perpendicular to the loop. The radius of the loop is made to shrink at a constant rate of 1 mms^-1. The induced emf when the radius is 2 cm is:

1. 2$\pi \mu$V

2. $\pi \mu$V

3. $\frac{\pi }{2}\mu V$

4. 2$\mu$V

An electron moves on a straight-line path XY as shown. The abcd is a coil adjacent to the path of electrons. What will be the direction of current if any, induced in the coil? 
,

1. abcd

2. adcb

3. The current will reverse its direction as the electron goes past the coil

4. No current included

The primary and secondary coils of a transformer have 50 and 1500 turns respectively. If the magnetic flux ϕ linked with the primary coil is given by ϕ=${\varphi }_0$+4t, where ϕ is in weber, t is time in second and ϕ₀is a constant, the output voltage across the secondary coil is:

1. 90 V

2. 120 V

3. 220 V

4. 30 V

A uniform magnetic field is restricted within a region of radius r. The magnetic field changes with time at a rate $\frac{dB}{dt}$. Loop 1 of radius R > r encloses the region r and loop 2 of radius R is outside the region of the magnetic field as shown in the figure. Then, the emf generated is:

1.  Zero in loop 1 and zero loop 2

2.  $-\frac{dB}{dt}\pi r^2$ in loop 1 and zero in loop 2

3.  $-\frac{dB}{dt}\pi R^2$ in loop 1 and zero in loop 2

4.  Zero in loop 1 and not defined in loop 2

The key K is inserted at time t= 0. The initial (t=0) and final $\left(t\to \infty \right)$ currents through battery are :

1. $\frac{1}{15}Amp, \frac{1}{10}Amp$

2. $\frac{1}{10}Amp, \frac{1}{15}Amp$

3. $\frac{2}{15}Amp, \frac{1}{10}Amp$

4. $\frac{1}{15}Amp, \frac{2}{25}Amp$

A current-carrying wire is placed below a coil in its plane, with current flowing as shown.

If the current increases –

1. no current will be induced in the coil 

2. an anticlockwise current will be induced in the coil 

3. a clockwise current will be induced in the coil 

4. the current induced in the coil will be first anticlockwise and then clockwise

Some magnetic flux is changed from a coil of resistance 10 ohm. As a result an induced current is developed in it, which varies with time as shown in figure. The magnitude of change in flux through the coil in webers is

(1) 2

(2) 4

(3) 6

(4) None of these