Alternating Current Test

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Alternating Current Test - 28

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Weekly Quiz Competition

Question 1
1 / -0

In a series $$LCR\, AC$$ circuit, the current is maximum when the impedance is equal to:

A
the reactance

B
the resistance

C
zero

D
twice the reactance

E
twice the resistance

Solution

In L-C-R circuit, the current
$$I=\displaystyle\frac{E_0}{\sqrt{R^2+(X_L-X_C)^2}}$$
When impedance $$Z=R$$, i.e., $$X_L=X_C$$ the current in the L-C-R circuit will be maximum.
Question 2
1 / -0

In an oscillating system, a restoring force is a must. In an L-C circuit, the restoring force is provided by a/an

A
inductor

B
capacitor

C
resistor

D
both A and B

Solution
Question 3
1 / -0

Alternating current is flowing in inductance $$L$$ and resistance $$R$$. The frequency of source is $$\omega/2\pi$$ Which of the following statement in correct:

A
For low frequency the limiting value of impedance is $$L$$.

B
For high frequency the limiting value of impedance is $$\omega L$$.

C
For high frequency the limiting value of impedance is $$R$$.

D
For low frequency the limiting value of impedance is $$\omega L$$.

Solution
Question 4
1 / -0

If we increase the driving frequency in a circuit with a purely resistive load, then amplitude $$V_R$$

A
remain in the same

B
increase

C
decrease

D
none

Solution

We know that $$V_R$$ does not depend on driving frequency in a purely resistive circuit.So,If we increase the driving frequency in a circuit with a purely resistive load, then amplitude remain in the same.
Therefore, A is correct option.
Question 5
1 / -0

The ratio of peak value and r.m.s value of an alternating current is

A
$$ 1 $$

B
$$ \dfrac{1}{2} $$

C
$$ \sqrt{2} $$

D
$$ \dfrac{1}{\sqrt{2}} $$

Solution

As we know,
$$V_0=V_{rms} \times \sqrt 2$$
so,
$$\dfrac{V_0}{V_{rms}}=\sqrt 2$$
Question 6
1 / -0

Current in the circuit is wattless, if

A
Inductance in the circuit is zero

B
Resistance in the circuit is zero

C
Current is alternating

D
Resistance and inductance both are zero

Solution

Current in the circuit is wattless,
Because power = $$ i^2R $$ , if $$ R = 0 $$ , then $$ P = 0 $$.
Question 7
1 / -0

The power factor of L-R circuit is :

A
$$\dfrac{R}{\omega L}$$

B
$$\dfrac{R}{(\omega L)^2+R^2}$$

C
$$\omega LR$$

D
$$\sqrt{\omega LR}$$

Solution
Question 8
1 / -0

Statement A: With an increase in the frequency of AC supply inductive reactance increases.
Statement B: With an increase in the frequency of AC supply capacitive reactance increase.

A
A is true but B is false

B
Both A and B are true

C
A is false but B is true

D
Both A and B are false

Solution

$$Z_L=WL$$ $$Z_C=\dfrac{1}{wc}$$

$$w\uparrow, Z_L\uparrow Z_c\downarrow$$
Question 9
1 / -0

In series L-C-R resonant circuit, to increase the resonant frequency :

A
L will have to be increased

B
C will have to be increased

C
LC will have to be decreased

D
LC will have to be increased

Solution

Resonant frequency $$=\dfrac{1}{\sqrt{LC}}$$

$$LC \downarrow \ if \ \omega_r \uparrow$$
Question 10
1 / -0

At low frequency a condenser offers :

A
high impedance

B
low impedance

C
zero impedance

D
impedance of condenser is independent of frequency

Solution

$$Z=\dfrac{1}{wc}$$

$$w\downarrow Z\uparrow$$

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Re-Attempt Weekly Quiz Competition

Alternating Current Test - 28

Result

Alternating Current Test - 28

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Rank

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SHARING IS CARING

Question 1

the reactance

the resistance

zero

twice the reactance

twice the resistance

Solution

Question 2

inductor

capacitor

resistor

both A and B

Solution

Question 3

For low frequency the limiting value of impedance is $$L$$.

For high frequency the limiting value of impedance is $$\omega L$$.

For high frequency the limiting value of impedance is $$R$$.

For low frequency the limiting value of impedance is $$\omega L$$.

Solution

Question 4

remain in the same

increase

decrease

none

Solution

Question 5

$$ 1 $$

$$ \dfrac{1}{2} $$

$$ \sqrt{2} $$

$$ \dfrac{1}{\sqrt{2}} $$

Solution

Question 6

Inductance in the circuit is zero

Resistance in the circuit is zero

Current is alternating

Resistance and inductance both are zero

Solution

Question 7

$$\dfrac{R}{\omega L}$$

$$\dfrac{R}{(\omega L)^2+R^2}$$

$$\omega LR$$

$$\sqrt{\omega LR}$$

Solution

Question 8

A is true but B is false

Both A and B are true

A is false but B is true

Both A and B are false

Solution

Question 9

L will have to be increased

C will have to be increased

LC will have to be decreased

LC will have to be increased

Solution

Question 10

high impedance

low impedance

zero impedance

impedance of condenser is independent of frequency

Solution

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