CBSE Class 12 Physics Quiz | CBSE Class 12 Physics Short Questions & Answers

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Questions
41 For measurement of potential difference, a potentiometer is preferred over voltmeter because
A potentiometer does not take current from the circuit.
B potentiometer is cheaper than voltmeter.
C the resistance of potentiometer is less than voltmeter.
D potentiometer is more sensitive than voltmeter.

Answer: potentiometer does not take current from the circuit.
42 Which of the following is wrong? Resistivity of a conductor is
A independent of temperature.
B inversely proportional to temperature.
C independent of dimensions of conductor.
D less than resistivity of a semiconductor.

Answer: independent of temperature.
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43 Two cells of emf’s approximately 5 V and 10 V are to be accurately compared using a potentiometer of length 400 cm. [NCERT Exemplar]
A The battery that runs the potentiometer should have voltage of 8 V.
B The battery of potentiometer can have a voltage of 15 V and R adjusted so that the potential drop across the wire slightly exceeds 10 V.
C The first portion of 50 cm of wire itself should have a potential drop of 10 V.
D Potentiometer is usually used for comparing resistances and not voltages.

Answer: The battery of potentiometer can have a voltage of 15 V and R adjusted so that the potential drop across the wire slightly exceeds 10 V.
44 A resistance R is to be measured using a meter bridge. Student chooses the standard resistance S to be 100 Ω He finds the null point at l1 = 2.9 cm. He is told to attempt to improve the accuracy. Which of the following is a useful way? [NCERT Exemplar]
A He should measure l1 more accurately.
B He should change Sto 1000 Ω and repeat the experiment.
C He should change S to 3 Ω and repeat the experiment.
D He should give up hope of a more accurate measurement with a meter bridge.

Answer: He should change S to 3 Ω and repeat the experiment.
45 Consider a current carrying wire current I in the shape of a circle. Note that as the current progresses along the wire, the direction of j (current density) changes in an exact manner, while die current/remain unaffected. The agent that is essentially responsible for is
A source of emf.
B electric field produced by charges accumulated on the surface of wire.
C the charges just behind a given segment of wire which push them just the right way by repulsion.
D the charges ahead.

Answer: electric field produced by charges accumulated on the surface of wire.
46 Which of the following is not correct about cyclotron?
A It is a machine to accelerate charged particles or ions to high energies.
B Cyclotron uses both electric and magnetic fields in combination to increase the energy of charged particles.
C The operation of the cyclotron is based on the fact that the time for one revolution of an ion is independent of its speed or radius of its orbit.
D The charged particles and ions in cyclotron can move on any arbitrary path.

Answer: The charged particles and ions in cyclotron can move on any arbitrary path.
47 A charged particle is moving in a cyclotron, what effect on the radius of path of this charged particle will occur when the frequency of the ratio frequency field is doubled?
A It will remain unchanged.
B It will be increased by four times.
C It will be halved.
D It will also be doubled.

Answer: It will remain unchanged.
48 Two a-particles have the ratio of their velocities as 3 : 2 on entering the field. If they move in different circular paths, then the ratio of the radii of their paths is
A 3 : 2
B 4 : 9
C 2 : 3
D 9 : 4

Answer: 3 : 2
49 A charged particle is moving on circular path with velocity v in a uniform magnetic field B, if the velocity of the charged particle is doubled and strength of magnetic field is halved, then radius becomes
A 8 times
B 4 times
C 2 times
D None of these

Answer: 4 times
50 Which one of the following is correct statement about magnetic forces?
A Magnetic forces always obey Newton’s third law.
B Magnetic forces do not obey Newton’s third law.
C For very high current, magnetic forces obey Newton’s third law.
D Inside low magnetic field, magnetic forces obey Newton’s third law.

Answer: Magnetic forces do not obey Newton’s third law.
51 In an inertial frame of reference, the magnetic force on a moving charged particle is Its value in another inertial frame of reference will be
A remained same
B changed due to change in the amount of charge
C changed due to change in velocity of charged particle
D changed due to change in field direction

Answer: changed due to change in velocity of charged particle
52 A strong magnetic field is applied on a stationary electron. Then the electron
A moves in the direction of the field.
B remained stationary.
C moves perpendicular to the direction of the field.
D moves opposite to the direction of the field.

Answer: remained stationary.
53 A positive charge enters in a magnetic field and travels parallel to but opposite the field. If experiences
A an upward force.
B a downward force.
C an accelerated force.
D no force.

Answer: an accelerated force.
54 An electron is projected along the axis of a circular conductor carrying the same current. Electron will experience
A a force along the axis
B a force perpendicular to the axis.
C a force at an angle of 4° with axis.
D no force experienced.

Answer: no force experienced.
55 The gyro-magnetic ratio of an electron in an H-atom, according to Bohr model, is
A independent of which orbit it is in.
B neutral
C positive
D increases with the quantum number n.

Answer: independent of which orbit it is in.
56 A conducting circular loop of radius r carries a constant current i. It is placed in a uniform magnetic field B, such that B is perpendicular to the plane of the loop. The magnetic force acting on the loop is
A irB.
B 2πriB
C zero
D πriB

Answer: zero
57 If the beams of electrons and protons move parallel to each other in the same direction, then they
A attract each other.
B repel each other.
C no relation.
D neither attract nor repel.

Answer: repel each other.
58 A current loop placed in a non-uniform magnetic field experiences
A a force of repulsion.
B a force of attraction.
C a torque but not force.
D a force and a torque.

Answer: a force and a torque.
59 The maximum current that can be measured by a galvanometer of resistance 40 Ω is 10 mA. It is converted into voltmeter that can read upto 50 V. The resistance to be connected in the series with the galvanometer is
A 4960 Ω
B 5040 Ω
C 4050 Ω
D 2010 Ω

Answer: 4960 Ω
60 A current carrying closed loop of an irregular shape lying in more than one plane when placed in uniform magnetic field, the force acting on it
A will be more in the plane where its larger position is covered.
B is zero.
C is infinite.
D may or may not be zero.

Answer: is zero.
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