Which of the following combinations should be selected for better tuning of an LCR circuit used for communication?
1. \(R = 20~\Omega,~L= 1.5~\text{H}, ~C = 35~\mu \text{F}\)
2. \(R = 25~\Omega,~L= 2.5~\text{H}, ~C = 45~\mu \text{F}\)
3. \(R = 15~\Omega,~L= 3.5~\text{H}, ~C = 30~\mu \text{F}\)
4. \(R = 25~\Omega,~L= 1.5~\text{H}, ~C = 45~\mu \text{F}\)
An inductor of reactance \(1~\Omega\) and a resistor of \(2~\Omega\) are connected in series to the terminals of a \(6~\text{V}\) (RMS) AC source. The power dissipated in the circuit is:
1. \(8~\text{W}\)
2. \(12~\text{W}\)
3. \(14.4~\text{W}\)
4. \(18~\text{W}\)
The output of a step-down transformer is measured to be 24 V when connected to a 12 W light bulb. The value of the peak current is:
1. 1/ A
2. A
3. 2 A
4. 2A
As the frequency of an AC circuit increases, the current first increases and then decreases. What combination of circuit elements is most likely to comprise the circuit?
(a) | Inductor and capacitor |
(b) | Resistor and inductor |
(c) | Resistor and capacitor |
(d) | Resistor, inductor, and capacitor |
Choose the correct options:
1. (b), (c)
2. (c), (d)
3. (b), (d)
4. (a), (d)
In an alternating current circuit consisting of elements in series, the current increases on increasing the frequency of the supply. Which of the following elements are likely to constitute the circuit?
(a) | Only resistor |
(b) | Resistor and an inductor |
(c) | Resistor and a capacitor |
(d) | Only a capacitor |
Choose the correct options:
1. (b), (c)
2. (a), (d)
3. (b), (d)
4. (c), (d)
Electrical energy is transmitted over large distances at high alternating voltages. Which of the following statements is (are) correct?
(a) | For a given power level, there is a lower current. |
(b) | Lower current implies less power loss. |
(c) | Transmission lines can be made thinner. |
(d) | It is easy to reduce the voltage at the receiving end using step-down transformers. |
1. (a), (b), (c)
2. (a), (b), (d)
3. (b), (c), (d)
4. (c), (d)
For an L-C-R circuit, the power transferred from the driving source to the driven oscillator is .
(a) | Here, the power factor cosϕ ≥ 0 , P ≥ 0 . |
(b) | The driving force can give no energy to the oscillator (P = 0) in some cases. |
(c) | The driving force cannot syphon out (P<0) the energy out of the oscillator. |
(d) | The driving force can take away energy out of the oscillator. |
Choose the correct options:
1. (a), (b), (c)
2. (a), (c,) (d)
3. (b), (c), (d)
4. (c), (d)
When an AC voltage of 220 V is applied to the capacitor C
(a) | the maximum voltage between plates is 220 V. |
(b) | the current is in phase with the applied voltage. |
(c) | the charge on the plates is in phase with the applied voltage. |
(d) | power delivered to the capacitor is zero. |
Choose the correct options:
1. (b), (c)
2. (a), (d)
3. (b), (d)
4. (c), (d)
The line that draws power supply to your house from the street has
(a) | zero average current |
(b) | 220 V average voltage |
(c) | voltage and current out of phase by \(90^\circ\) |
(d) | voltage and current possibly differing in phase \(\phi\) such that \(|\phi|<\dfrac \pi 2\) |
Choose the correct options:
1. (b), (c)
2. (a), (d)
3. (b), (d)
4. (a), (c)
When a voltage measuring device is connected to AC mains, the meter shows the steady input voltage of \(220~\text{V}\). This means:
1. | input voltage cannot be AC voltage, but a DC voltage |
2. | maximum input voltage is \(220~\text{V}\) |
3. | the meter reads not v but \(<v^2>\) and is calibrated to read \(\sqrt{<v^2>}\) |
4. | the pointer of the meter is stuck by some mechanical defect |