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Alternating Current Physics - Alternating Current

Jharkhand Board (JAC) - STD 12 Science - Physics (Jharkhand - English Medium). 460 questions in this chapter.

Question types

Alternating Current question types

460 questions across 7 question groups — pick any mix to generate a Physics paper with step-by-step answer keys.

460
Questions
7
Question groups
5
Question types
Sample Questions

Alternating Current questions

One sample from each question group in this chapter. Select any group above to see the full set with answer keys.

Q 1M.C.Q (1 Marks)1 Mark
The line that draws power supply to your house from street has:
  • A
    Zero average current.
  • B
    220V average voltage.
  • ✓
    A and D both.
  • D
    Voltage and current possibly differing in phase $\phi$ such that $\Big|\phi\Big|<\frac{\pi}{2}$.

Answer: C.

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Q 2M.C.Q (1 Marks)1 Mark
When a voltage measuring device is connected to $AC$ mains, the meter shows the steady input voltage of $220V$. This means,
  • A
    Input voltage cannot be $AC$ voltage, but a $DC$ voltage.
  • B
    Maximum input voltage is $220V.$
  • ✓
    The meter reads not v but $\left\langle v^2\right\rangle a$ and is calibrated to read $\sqrt{<\text{v}^2>}$.
  • D
    The pointer of the meter is stuck by some mechanical defect.

Answer: C.

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Q 3M.C.Q (1 Marks)1 Mark
The diagram given show the variation of voltage and current in an $AC$ circuit. The circuit contains.
Image
  • A
    Only a resistor
  • ✓
    Only a pure inductor
  • C
    Only a capcacitor
  • D
    A capacitor and and inductor

Answer: B.

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Q 5M.C.Q (1 Marks)1 Mark
To reduce the reasonant frequency in an $\text{LCR}$ series circuit with a generator:
  • A
    The generator frequency should be reduced.
  • ✓
    Another capacitor should be added in parallel to the first.
  • C
    The iron core of the inductor should be removed.
  • D
    Dielectric in the capacitor should be removed.

Answer: B.

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Q 6Assertion (A) & Reason (B) MCQ1 Mark
For two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
  1. Both A and R are true and R is the correct explanation of A.
  2. Both A and R are true but R is not the correct explanation of A.
  3. A is true but R is false.
  4. A is false and R is also false.
Assertion: An alternating current shows magnetic effect.
Reason: Magnitude of alternating current varies with time.
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Q 7Assertion (A) & Reason (B) MCQ1 Mark
For two statements are given-one labelled Assertion $(A)$ and the other labelled Reason $(R)$. Select the correct answer to these questions from the codes $(a), (b), (c)$ and $(d)$ as given below.
Assertion: A bulb connected in series with a solenoid is connected to $A.C.$ source. If a soft iron core is introduced in the solenoid, the bulb will glow brighter.
Reason: On introducing soft iron core in the solenoid, the inductance decreases.
  • A
    Both $A$ and $R$ are true and $R$ is the correct explanation of $A$.
  • B
    Both $A$ and $R$ are true but $R$ is not the correct explanation of $A.$
  • C
    $A$ is true but $R$ is false.
  • ✓
    $A $ is false and $R$ is also false.

Answer: D.

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Q 8Assertion (A) & Reason (B) MCQ1 Mark
For two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
  1. Both A and R are true and R is the correct explanation of A.
  2. Both A and R are true but R is not the correct explanation of A.
  3. A is true but R is false.
  4. A is false and R is also false.
Assertion: The alternating current lags behind the e.m.f. by a phase angle of $\frac{\pi}{2}$ when A.C. flows through an inductor.
Reason: The inductive reactance increases as the frequency of A. C. source decreases.
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Q 9Assertion (A) & Reason (B) MCQ1 Mark
For two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
  1. Both A and R are true and R is the correct explanation of A.
  2. Both A and R are true but R is not the correct explanation of A.
  3. A is true but R is false.
  4. A is false and R is also false.
Assertion: An inductance and a resistance are connected in series with an A.C. circuit. ln this circuit the current and the potential difference across the resistance lags behind potential difference across the inductance by an angle $\frac{\pi}{2}.$
Reason: In L-R circuit voltage leads the current by phase angle which depends on the value ofinductance and resistance both.
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Q 10Assertion (A) & Reason (B) MCQ1 Mark
For two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
  1. Both A and R are true and R is the correct explanation of A.
  2. Both A and R are true but R is not the correct explanation of A.
  3. A is true but R is false.
  4. A is false and R is also false.
Assertion: Long distance transmission of A.C. is carried out at extremely high voltage.
Reason: For large distance, voltage has to be large.
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Q 151 Marks Question1 Mark
What is the amount of work done in moving a point charge Q around a circular arc of radius ‘r' at the centre of which another point charge ‘q' is located?
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Q 162 Marks Questions2 Marks
A small town with a demand of 800kW of electric power at 220V is situated 15km away from an electric plant generating power at 440V. The resistance of the two wire line carrying power is 0.5Ω per km. The town gets power from the line through a 4000-220V step-down transformer at a sub-station in the town.
  1. Estimate the line power loss in the form of heat.
  2. How much power must the plant supply, assuming there is negligible power loss due to leakage?
  3. Characterise the step up transformer at the plant.
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Q 172 Marks Questions2 Marks
Write briefly the underlying principle used in Davison-Germer experiment to verify wave nature of electrons experimentally. What is the de-Broglie wavelength of an electron with kinetic energy (of).120 ev? Write briefly the underlying principle used in Davison-Germer experiment to verify wave nature of electrons experimentally. What is the de-Broglie wavelength of an electron with kinetic energy (of).120 ev?
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Q 202 Marks Questions2 Marks
  1. Distinguish between ‘Analog’ and ‘Digital’ forms of communication.
  2. Explain briefly two commonly used applications of the ‘Internet’.
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Q 223 Marks Question3 Marks
A series LCR circuit with R = 20Ω, L = 1.5H and C = 35μF is connected to a variable-frequency 200V ac supply. When the frequency of the supply equals the natural frequency of the circuit, what is the average power transferred to the circuit in one complete cycle?
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Q 233 Marks Question3 Marks
A radio can tune over the frequency range of a portion of MW broadcast band: (800kHz to 1200kHz). If its LC circuit has an effective inductance of 200μH, what must be the range of its variable capacitor?
[Hint: For tuning, the natural frequency i.e., the frequency of free oscillations of the LC circuit should be equal to the frequency of the radiowave.]
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Q 243 Marks Question3 Marks
Obtain the resonant frequency and Q-factor of a series LCR circuit with L = 3.0H, C = 27μF, and R = 7.4Ω. It is desired to improve the sharpness of the resonance of the circuit by reducing its ‘full width at half maximum’ by a factor of 2. Suggest a suitable way.
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Q 265 Marks Questions5 Marks
A small town with a demand of 800kW of electric power at 220V is situated 15km away from an electric plant generating power at 440V. The resistance of the two wire line carrying power is 0.5Ω per km. The town gets power from the line through a 4000-220V step-down transformer at a sub-station in the town.
  1. Estimate the line power loss in the form of heat.
  2. How much power must the plant supply, assuming there is negligible power loss due to leakage?
  3. Characterise the step up transformer at the plant.
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Q 275 Marks Questions5 Marks
During a thunderstorm the ‘live' wire of the transmission line fell down on the ground. A group of boys passing through noticed it and some of them wanted to place the wire by the side. As they were approaching the wire and trying to lift it, Bari noticed it and immediately pushed them away to prevent them from touching the wire. Two of them got hunt in the process. Bari took them to a doctor to get medical aid.
Based on the above paragraph, answer the following:
  1. Write two values which Bari displayed during the incident.
  2. Why is it that a bird can sit over a suspended ‘live' wire without any harm whereas touching it on the ground can give a fatal shock?
  3. The electric power from a power plant is set up to a very high voltage before transmitting it to distant consumers. Write the reason for it.
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Q 285 Marks Questions5 Marks
Hari is a student of Class X in a school near his village. His uncle gifted him a bicycle with a dynamo fitted in it. He was thrilled to find that while cycling during night, he could light the bulb and see the objects on the road clearly. He, however, did not know how this device works. He asked this question to his teacher. The teacher considered it an opportunity and explained the working of a dynamo to the whole class.
Answer the following questions:
  1. State the principle and working of a dynamo.
  2. Write two values each displayed by Hari and his Science teacher.
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Q 295 Marks Questions5 Marks
Shiv had a high tension tower erected on his farm land. He kept complaining to the authorities to remove it since it occupied a large portion of his land. His uncle, who was a teacher, explained to him the need for erecting these towers for efficient transmission of power. As Shiv got convinced and realised significance, he stopped complaining.
Based on the above paragraph, answer the following questions:
  1. Why is it necessary to transport power at high voltages?
  2. ‘A low power factor implies large power loss'. Explain.
  3. Write the two values displayed by Shiv and his Uncle.
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Q 305 Marks Questions5 Marks
Seema's uncle was advised by his doctor to have an MRI (Magnetic Resonance Imaging) scan of his brain. Her uncle felt it to be expensive and wanted to postpone it. When Seema learnt about this, she took the help of her family and also approached the doctor, who also offered a substantial discount. She then convinced her uncle to undergo the test to enable the doctor to know the condition of his brain. The information thus obtained greatly helped the doctor to treat him properly.
Based on the above paragraph, answer the following questions:
  1. What according to you are the values displayed by Seema, her family and the doctor?
  2. What could be the possible reason for MRI test to be so expensive?
  3. Assuming that MRI test was performed using a magnetic field of 0.1 T., find the minimum and maximum values of the force that the magnetic field could exert on a proton $($charge $= 1.6 x 10^{-19} C)$ moving with a speed of $10^4$ m/s.
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Q 31Case study (4 Marks)4 Marks
A capacitor'C', a variable resistor 'R' and a bulb 'B' are connected in series to the ac mains in circuit as shown. The bulb glows with some brightness. How will the glow of the bulb change if (i) a dielectric slab is introduced between the plates of the capacitor, keeping resistance R to be the same; (ii) the resistance R is increased keeping the same capacitance?
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Q 32Case study (4 Marks)4 Marks
The household supply of electricity is at 220V (rms value) and 50Hz. Find the peak voltage and the least possible time in which the voltage can change from the rms value to zero.
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Q 33Case study (4 Marks)4 Marks
An LC circuit also called a resonant circuit, tank circuit or tuned circuit is an electric circuit consisting of an inductor represented by the letter Land a capacitor, represented by the letter C connected together. An LC circuit is an idealized model since it assumes there is no dissipation of energy due to resistance. An LC circuit contains a 20mH inductor and a $50\mu\text{F}$ capacitor with an initial charge of 10mC. The resistance of the circuit is negligible. Let the instant the circuit is closed bet = 0.
  1. The total energy stored initially is:
  1. 5J
  2. 3J
  3. 10J
  4. 1J
  1. The natural frequency of the circuit is:
  1. 159.24Hz
  2. 200.12Hz
  3. 110.25Hz
  4. 95Hz
  1. At what time is the energy stored completely electrical?
  1. $0, 5\text{T}, 9\text{T}$
  2. $0,\text{T}, 2\text{T}, 3\text{T}$
  3. $\frac{\text{T}}{2},\frac{\text{5T}}{2},\frac{\text{9T}}{2}$
  4. $0,\frac{\text{T}}{2},{\text{T}},\frac{\text{3T}}{2}$
  1. At what time is the energy stored completely magnetic?
  1. $\frac{\text{T}}{2},\frac{\text{3T}}{2},\frac{\text{T}}{4}$
  2. $\frac{\text{T}}{3},\frac{\text{T}}{9},\frac{\text{T}}{12}$
  3. $0, 2\text{T}, 3\text{T}$
  4. $\frac{\text{T}}{4},\frac{\text{3T}}{4},\frac{\text{5T}}{4}$
  1. The value of $X_L$ is:
  1. $20\Omega$
  2. $40\Omega$
  3. $60\Omega$
  4. $50\Omega$
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Q 34Case study (4 Marks)4 Marks
Let a source of alternating e.m.f. $\text{E} = \text{E}_\circ\sin\omega\text{t}$ be connected to a circuit containing a pure inductance L. If I is the value of instantaneous current in the circuit, then $\text{I}=\text{I}_\circ\sin\Big(\omega\text{t}-\frac{\pi}{2}\Big).$ The inductive reactance limits the current in a purely inductive circuit and is given by $\text{X}_\text{L}= \text{W}_\text{L}.$
  1. A 100 hertz a.c. is flowing in a 14mH coil. The reactance is:
  1. $15\Omega$
  2. $7.7\Omega$
  3. $8.8\Omega$
  4. $10\Omega$
  1. In a pure inductive circuit, resistance to the flow of current is offered by:
  1. Resistor
  2. Inductor
  3. Capacitor
  4. Resistor and inductor
  1. In a inductive circuit, by what value of phase angle does alternating current lags behind e.m.f.?
  1. 45º
  2. 90º
  3. 120º
  4. 75º
  1. How much inductance should be connected to 200V, 50Hz a.c. supply so that a maximum current of 0.9A flows through it?
  1. 5H
  2. 1H
  3. 10H
  4. 4.5H
  1. The maximum value of current when inductance of 2H is connected to 150V, 50Hz supply is:
  1. 0.337A
  2. 0.721A
  3. 1.521A
  4. 2.522A
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Q 35Case study (4 Marks)4 Marks
Step-down transformers are used to decrease or step-down voltages. These are used when voltages need to be lowered for use in homes and factories. A small town with a demand of 800kW of electric power at 220V is situated 15km away from an electric plant generating power at 440V. The resistance of the two wire line carrying power is 0.5Q per km. The town gets power from the line through a 4000 - 220V step-down transformer at a sub-station in the town.
  1. The value of total resistance of the wires is:
  1. $25\Omega$
  2. $30\Omega$
  3. $35\Omega$
  4. $15\Omega$
  1. The line power loss in the form of heat is:
  1. 550kW
  2. 650kW
  3. 600kW
  4. 700kW
  1. How much power must the plant supply, assuming there is negligible power loss due to leakage?
  1. 600kW
  2. 1600kW
  3. 500W
  4. 1400kW
  1. The voltage drop in the power line is:
  1. 1700V
  2. 3000V
  3. 2000V
  4. 2800V
  1. The total value of voltage transmitted from the plant is:
  1. 500V
  2. 4000V
  3. 3000V
  4. 7000V
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