In which of the following devices, the eddy current effect is not used?

1. electric heater

2. induction furnace

3. magnetic braking in train

4. electromagnet

A 800 turn coil of effective area 0.05 $m^2$ is kept perpendicular to a magnetic field $5\times {10}^{-5} T$. When the plane of the coil is rotated by 90$°$ around any of its coplanar axis in 0.1 s, the emf induced in the coil will be:

1. 0.02V

2. 2 V

3. 0.2 V

4. $2\times {10}^{-3} V$

A cycle wheel of radius 0.5 m is rotated with a constant angular velocity of 10 rad/s in a region of a magnetic field of 0.1 T which is perpendicular to the plane of the wheel. The EMF generated between its centre and the rim is:

(1) 0.25 V

(2) 0.125 V

(3) 0.5 V

(4) zero

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