Apparent Power

Q. The magnetic field energy in an inductor changes from maximum value to minimum value in 5 ms when connected to an AC source. The frequency of the source is

1. $20\text{Hz}$
2. $50\text{Hz}$
3. $20\text{Hz}$
4. $500\text{Hz}$

Q. A variable voltage $V=2t$ is applied across an inductor of inductance $L=2\text{H}$ as shown in figure. Then

1. Current versus time graph is a parabola.
2. Energy stored in magnetic field at $t=2\text{s}$ is $4\text{J}$.
   
3. Potential energy at time $t=1\text{s}$ in magnetic field is increasing at a rate of $1\text{J/s}$.
4. Energy stored in magnetic field is zero in all time.

Q.

An AC source is rated at $220V,50Hz$. The time taken for voltage to change from its peak value to zero is

1. $50sec$

2. $0.02sec$

3. $5sec$

4. $5x{10}^{-3}sec$

Q. Two coils, held in fixed position have a mutual inductance of 70 μH, one coil carries current $50sin\left(100\pi t\right)$ and other coil has resistance $8\pi$ $\Omega$, find peak current in other coil.

1. $\frac{7}{160}$ A
2. $\frac{3}{160}$ A
3. $\frac{5}{160}$ A
4. $\frac{9}{160}$ A

Q. Two tuning forks P and Q are vibrated together. The number of beats produced are represented by the straight line OA in the following graph. After loading Q with wax again these are vibrated together and the beats produced are represented by the line OB. If the frequency of P is 341 Hz, the frequency of Q will be:

1. 341 Hz
2. 338 Hz
3. 344 Hz
4. 330 Hz

Q. The vibrations of four air columns are represented in the figure. The ratio of frequencies np :nq : nr : ns is

1. 12 : 6 : 3 : 5
2. 6 : 2 : 3 : 4
3. 1 : 2 : 4 : 3
4. 4 : 2 : 3 : 1

Q. Match the Column I with Column II

	Column I (Physical quantity)		Column II (Name of unit)
(A)	Conductance	(p)	gray
(B)	Magnetic induction	(q)	lumen
(C)	Absorbed dose	(r)	tesla
(D)	Luminous flux	(s)	siemens

1. A - s, B - r, C - p, D - q.
2. A - p, B - q, C - r, D - s.
3. A - r, B - s, C - p, D - q.
4. A - q, B - p, C - s, D - r.

Q. The magnetic field energy in an inductor changes from maximum value to minimum value in 5 ms when connected to an AC source. The frequency of the source is

1. $20\text{Hz}$
2. $50\text{Hz}$
3. $20\text{Hz}$
4. $500\text{Hz}$

Q. The magnetic field energy in an inductor changes from maximum value to minimum value in 5 ms when connected to an AC source. The frequency of the source is

1. $20\text{Hz}$
2. $50\text{Hz}$
3. $20\text{Hz}$
4. $500\text{Hz}$

Q. The vibrations of 4 air columns are as shown in the figure. The ratio of the frequencies $n_p:n_q:n_r:n_s$

1. 12 : 6 : 3 : 4
2. 1 : 2 : 4 : 3
3. 4 : 2 : 3 : 1
4. 6 : 2 : 3 : 4

Q. The magnetic field energy in an inductor changes from maximum value to minimum value in 5 ms when connected to an AC source. The frequency of the source is

1. $20\text{Hz}$
2. $50\text{Hz}$
3. $20\text{Hz}$
4. $500\text{Hz}$