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# Test: Power in an AC Circuit

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## 10 Questions MCQ Test Physics Class 12 | Test: Power in an AC Circuit

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Test: Power in an AC Circuit - Question 1

### Find the total voltage applied in a series RLC circuit when i=3mA, VL=30V, VC=18V and R=1000 ohms.

Detailed Solution for Test: Power in an AC Circuit - Question 1

Explanation: Total voltage= VR+VL+VC.
VR=1000x3x10-3=3V.
Therefore, total voltage = 30+18+3=51V.

Test: Power in an AC Circuit - Question 2

### The power factor of an RL circuit 1/root2. If the frequency of a.c. is doubled, what will be the power factor?​

Detailed Solution for Test: Power in an AC Circuit - Question 2 Test: Power in an AC Circuit - Question 3

### When an emf E = 7cos wt is applied across a circuit, the current is I = 5coswt. What is the power factor for the circuit?

Detailed Solution for Test: Power in an AC Circuit - Question 3

Since E and I are in the same phase.
Therefore, phase difference will be 0 and since power factor= cosx (where x= phase difference) and x =0
therefore, cos x or power factor will be =1

Test: Power in an AC Circuit - Question 4

What is value of power factor if Ø = 90°​

Detailed Solution for Test: Power in an AC Circuit - Question 4

P=Irms Vrms cos ϕ
Where, ϕ=90
cosϕ=0
therefore,P=0
hence the correct answer is option A.

Test: Power in an AC Circuit - Question 5

Power in an ac circuit is equal to

Test: Power in an AC Circuit - Question 6

If the instantaneous current in a circuit is given by i = 2 cos (ωt - φ) A, the rms value of the current is

Detailed Solution for Test: Power in an AC Circuit - Question 6

i=2cost
=Im​cost
So, Im​=2amp
IRMS​=Im​​/√​2​
=2/√​2​
=2​amp

Test: Power in an AC Circuit - Question 7

Find the true power given apparent power = 10 W and power factor = 0.5​

Detailed Solution for Test: Power in an AC Circuit - Question 7

The formula of true power is,
True power=Apparent power x power factor
So, true power=10 x 0.5
True power=5W

Test: Power in an AC Circuit - Question 8

What is the average power/cycle in a capacitor?​

Detailed Solution for Test: Power in an AC Circuit - Question 8

The average power consumed/cycle in an ideal capacitor is 0.
The average power consumed in an ideal capacitor is given as based on the instantaneous power which is supplied to the capacitor:
pc = iv= (im cos ωt)(vm sin ωt)
pc = imvm (cos ωt sin ωt)
pc=(imvm/2)sin2ωt
We know that sin ωt = 0
Therefore, average power = 0

Test: Power in an AC Circuit - Question 9

What is phase angle given R = 10, Z = 20​

Detailed Solution for Test: Power in an AC Circuit - Question 9

Cos x (power factor) = R/Z
= 10/20
=1/2
x= 60

Test: Power in an AC Circuit - Question 10

In a circuit, the reactance X and resistance R are equal. What is the power factor?​

Detailed Solution for Test: Power in an AC Circuit - Question 10

Given that,
Reactance (X) =Resistance (R)
tanϕ = X/R​
So, we have ϕ = π/4​
Power factor = cosϕ = ​1​/√2

## Physics Class 12

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## Physics Class 12

157 videos|452 docs|213 tests

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