An aluminum ring B faces an electromagnet A. The current I through A can be altered. Then :

 

(1) Whether I increases or decreases, B will not experience any force

(2) If I decrease, A will repel B

(3) If I increases, A will attract B

(4) If I increases, A will repel B

Figure shows three regions of magnetic field, each of area A, and in each region magnitude of magnetic field decreases at a constant rate $\mathrm{\alpha }$.

If $\overrightarrow{\mathrm{E}}$ is induced electric field then value of line integral $\int \overrightarrow{\mathrm{E}}.\mathrm{d}\overrightarrow{\mathrm{r}}$ along the given loop is equal to

1.  $\mathrm{\alpha A}$                             

2.  $-\mathrm{\alpha A}$

3.  $3\mathrm{\alpha A}$                           

4.  $-3\mathrm{\alpha A}$

The magnitude of the earth’s magnetic field at a place is B₀ and the angle of dip is δ. A horizontal conductor of length l lying along the magnetic north-south moves eastwards with a velocity v. The emf induced across the conductor is 

(1) Zero

(2) B₀lv sinδ

(3) B₀lv

(4) B₀lv cosδ

The figure shows three circuits with identical batteries, inductors, and resistors. Rank the circuits according to the current through the battery (i) just after the switch is closed and (ii) a long time later, greatest first

(1) (i) i₂ > i₃ > i₁ (i₁ = 0) (ii) i₂ > i₃ > i₁

(2) (i) $i_2<i_3<i_1(i_1\ne 0)$ (ii) i₂ > i₃ > i₁

(3) (i) i₂ = i₃ = i₁ (i₁ = 0) (ii) i₂ < i₃ < i₁

(4) (i) $i_2=i_3>i_1(i_1\ne 0)$ (ii) i₂ > i₃ > i₁

An e.m.f. of 15 volt is applied in a circuit containing 5 henry inductance and 10 ohm resistance. The ratio of the currents at time t = ∞ and at t = 1 second is 

(1) $\frac{e^{1/2}}{e^{1/2}-1}$

(2) $\frac{e^2}{e^2-1}$

(3) 1 – e^–1

(4) e^–1

Consider the situation shown in the figure. The wire AB is sliding on the fixed rails with a constant velocity. If the wire AB is replaced by semicircular wire, the magnitude of the induced current will 

(1) Increase

(2) Remain the same

(3) Decrease

(4) Increase or decrease depending on whether the semicircle bulges towards the resistance or away from it

The self inductance of a coil is L. Keeping the length and area same, the number of turns in the coil is increased to four times. The self inductance of the coil will now be 

(1) $\frac{1}{4}L$

(2) L

(3) 4 L

(4) 16 L

A thin semi-circular conducting ring of radius R is falling with its plane vertical in a horizontal magnetic induction $\overrightarrow{\mathrm{B}}$ (see figure).

At the position MNQ the speed of the ring is v and the potential difference developed across the ring is

1. zero 

2. ${\mathrm{Bv\pi R}}^2 /2$ and M is at higher potential 

3. $\mathrm{\pi RBv}$ and Q is at higher potential 

4. $2\mathrm{RBv}$ and Q is at higher potential.

The current i in an induction coil varies with time t according to the graph shown in figure. Which of the following graphs shows the induced emf (e) in the coil with time

(1)

(2)

(3)

(4)

A uniform but time-varying magnetic field $\mathrm{B}\left(\mathrm{t}\right)$ exists in a circular region of radius $\mathrm{a}$ and is directed into the plane of the paper, as shown.

The magnitude of the induced electric field at point $\mathrm{P}$ at a distance $\mathrm{r}$ from the centre of the circular region :

1.  is zero                             

2.  decreases as $1/\mathrm{r}$ 

3.  increases as $\mathrm{r}$               

4.  decreases as $1/{\mathrm{r}}^2$