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Physics Assertion (A) & Reason (B) MCQ

Current Electricity · Uttarakhand Board (UBSE) STD 12 Science (Uttarakhand - English Medium). 20 questions.

Questions

Assertion (A) & Reason (B) MCQ

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20 questions · 4 auto-graded MCQ + 16 self-marked written.

Question 11 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 temperature coefficient of resistance is always positive only for metals.
Reason: On increasing the temperature, the resistance of metals and alloys increases.
Answer
  1. Both A and R are true, but R is not the correct explanation of A.
Explanation:

The value of temperature coefficient of resistance is positive only for metals and alloys and is negative for semiconductors and insulators.
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Question 21 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: Insulator do not allow flow of current through them.
Reason: Insulator have no free charge carrier.
Answer
  1. Both A and R are true, and R is the correct explanation of A.
Explanation:

Since current arises due to continuous flow of charged particles. There is no free charge in insulator hence no flow of charges are possible. Therefore current do not ftow through insulators.
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Question 31 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: A person touching a high power line gets stuck with the line.
Reason: The current carrying wire attracts the man towards it.
Answer
  1. A is false, and R is also false.
Explanation:

Because there is no special attractive force that keeps a person stuck with a high power line. The actual reason is that a current of the order of 0.05A or even less is enough to bring disorder in our nervous system. As a result of it, the affected person may lose temporarily his ability to control his nervous system to get himself free from the high power tine.
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Question 41 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: Fuse wire must have high resistance and low melting point.
Reason: Fuse is used for small current flow only.
Answer
  1. A is true, but R is false.
Explanation:

Fuse wire must have high resistance because in series, current remains same. Therefore according to Joule's law $\text{H}=\frac{\text{i}^2\text{Rt}}{4.2},$ heat produced is high if R is high. The melting point must be low so that wire may melt with increase in temperature. As a current larger than the specified value flows through the circuit the temperature of the fuse wire increases. This melts the fuse wire and breaks the circuit.
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Question 51 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: KWhr is a commercial unit used for expressing consumed electric energy.
Reason: Kilo-watt hour is the unit of electric power.
Answer
  1. A is true, but R is false.
Explanation:

1kWhr = 1kW × 1 hour

= 1000 (joule/ sec) × 3600 sec = 36 × 105 joule i.e., kWhr is the unit of electric energy and used for expressing consumed electric energy.
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Question 61 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: Though the same current flows through the live wires and the filament of the bulb but heat produced in the filament is much higher than that in live wires.
Reason: The filament of bulbs is made of a material of high resistance and high melting point.
Answer
  1. Both A and R are true, but R is not the correct explanation of A.
Explanation:

As filament of bulb and live wire are in series, hence current through both is same. Now, because $\text{H}=\frac{\text{i}^2\text{Rt}}{4.2}$ and resistance of the filament of the bulb is much higher than that of live wires, hence heat produced in the filament is much higher than that in line wires.
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Question 71 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 200W bulbs glows with more brightness than 100W bulbs.
Reason: A 100 watt bulb has more resistance than a 200W bulb.
Answer
  1. Both A and R are true, but R is not the correct explanation of A.
Explanation:

The resistance, $\text{R}=\frac{\text{V}^2}{\text{p}},$ i.e., $\text{R}\propto\frac{1}{\text{P}}$ i.e., higher is the wattage of a bulb, lesser is the resistance and so it will glow bright.
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MCQ 81 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: The current flowing through a conductor is directly proportional to the drift velocity.
Reason: As the drift velocity increases the current following through the conductor 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 $A$.
     
  • ✓
    $A$ is true, but $R$ is false.
     
  • D
    $A$ is false, and $R$ is also false.
Answer
Correct option: C.
$A$ is true, but $R$ is false.
 
$A$ is true, but $R$ is false.
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Question 91 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: If the length of the conductor is doubled, the drift velocity will become half of the original value (keeping potential difference unchanged).
Reason: At constant potential difference, drift velocity is inversely proportional to the length of the conductor.
Answer
  1. Both A and R are true, and R is the correct explanation of A.
Explanation:

Drift velocity of free electrons is given by, $\text{v}_\text{d}=\frac{\text{eE}}{\text{m}}\tau$

Where, $\text{E}=\frac{\text{Potential difference }}{\text{ength }}=\frac{\text{V}}{\text{l}}$

$\therefore\text{v}_\text{d}=\frac{\text{eE}}{\text{ml}}\tau$ r.e., $\text{v}_\text{d}\propto\frac{\text{1}}{\text{l}}$ where, $\frac{\text{eV}\tau}{\text{m}}$ is constant.

It mean if l is doubled, the drift velocity will become half of the original value.
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MCQ 101 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: Two bulbs of same wattage, one having a carbon filament and the other having a metallic filament are connected in series. Metallic bulbs will glow more brightly than carbon filament bulb.
Reason: Carbon is a semiconductor.
  • 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
Correct option: D.
$A$ is false, and $R$ is also false.
$A$ is false, and $R$ is also false.
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Question 111 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: Material used in the construction of a standard resistance is constantan or manganin.
Reason: Temperature coefficient of constantan is very small.
Answer
  1. Both A and R are true, and R is the correct explanation of A.
Explanation:

These alloys (constantan or manganin) are used for making standard resistance because they possess high resistivity and low temperature coefficient of resistance.
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Question 121 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 average thermal velocity of the electrons in a conductor is zero.
Reason: Direction of motion of electrons are randomly oriented.
Answer
  1. Both A and R are true, and R is the correct explanation of A.
Explanation:

ln normal conductor, the direction of electrons are randomly oriented such that the total sum of their velocities is equal to zero.
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Question 131 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: Current is a scalar quantity.
Reason: Electric current arises due to continuous flow of charged particles or ions.
Answer
  1. Both A and R are true, but R is not the correct explanation of A.
Explanation:

Current is a scalar quantity, it is justified by the following two observations:
  1. If current carrying wire is bent at some point, then also current in the wire remains same, while a vector quantity always changes by changing its direction.
  2. Current flowing in the circuit do not follow the laws of vector addition. It follows according to ordinary rule of algebra. This makes it clear that current is not a vector but a scalar quantity. Also current is defined as rate of flow of charge through the wire $\text{I}=\frac{\text{dq}}{\text{dt}}.$
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Question 141 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 current in a wire is due to flow of free electrons in a definite direction.
Reason: A current carrying wire should have non-zero charge.
Answer
  1. A is true, but R is false.
Explanation:

The current in a wire is due to flow of free electrons in a definite direction. But the number of protons in the wire at any instant is equal to number of electrons and charge on electrons is equal and opposite to that of proton. Hence, net charge on the wire is zero.
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MCQ 151 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: Two electric bulbs of $50$ and $100$ watt are given. When connected in series $50$ watt bulb glows more but when connected in parallel $100$ watt bulb glows more.
Reason: In series combination, power is directly proportional to the resistance of circuit. But in parallel combination, power is inversely proportional to the resistance of the circuit.
  • ✓
    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.
     
  • D
    $A$ is false, and $R$ is also false.
Answer
Correct option: A.
Both $A$ and $R$ are true, and $R$ is the correct explanation of $A.$
 
Both $A$ and $R$ are true, and $R$ is the correct explanation of $A.$
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Question 161 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: Chemical reactions involved in primary cells are irreversible and in secondary cells are reversible.
Reason: Primary cells can be recharged, but secondary cells can not be recharged.
Answer
  1. A is true, but R is false.
Explanation:

Primary cells cannot be recharged because they involve irreversible reactions. Secondary cells can be recharged because they involve reversible reactions.
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MCQ 171 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: ln a chain of bulbs, $50$ bulbs are joined in series. One bulb is removed now the circuit is again completed. If the remaining $49$ bulbs are again connected in series across the same supply, then light gets decreased in the room.
Reason: The resistance of $49$ bulbs will be more than $50$ bulbs.
  • 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
Correct option: D.
$A$ is false and $R$ is also false.
Since the bulbs are joined in series, so when one bulb is removed from chain then the resistance of the chain is decreased, hence current flowing through each bulb is increased. As heat produced ee $i^2$, hence light gets increased in the room.
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Question 181 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: It is advantageous to transmit electric power at high voltage.
Reason: High voltage implies high current.
Answer
  1. A is true, but R is false.
Explanation:

As P = Vi, hence for the transmission of same power, high voltage implies less current. Therefore heat energy loses $\Big(\text{H} = \frac{\text{i}^2\text{Rt}}{4.2}\Big)$are minimized if power is transmitted at high voltage.
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Question 191 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 drift velocity of electrons in a metallic wire will decrease, if the temperature of the wire is increased.
Reason: On increasing temperature, conductance of metallic wire decreases.
Answer
  1. Both A and R are true, but R is not the correct explanation of A.
Explanation:

On increasing temperature of wire, the kinetic energy of free electrons increase and so they collide more rapidly with each other, and hence their drift velocity decreases. Also when temperature increases, resistance increase, and resistance is inversely proportional to conductivity of material.
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Question 201 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: Heater wire must have high resistance and high melting point.
Reason: If resistance is high, the electric conductivity will be less.
Answer
  1. Both A and R are true, but R is not the correct explanation of A.
Explanation:

Heater wire must have high resistance and high melting point, because in series current remains same, therefore according to Joule's law $\text{H} = \frac{\text{i}^2\text{Rt}}{4.2}$ heat produced is high if R is high. Melting point must be high, so that wire may not melt with increase in temperature.
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