Hall Effect Questions and Answers

Q: Force exerted by magnetic field in Hall effect transducer is :

The force is the Lorentz force.In a Hall effect transducer, charge carriers moving through a conductor or semiconductor in a magnetic field experience the force F = q(v × B). This Lorentz force pushes them to one side of the material, building up the Hall voltage across it, which the transducer measures.The Hall effect is the resulting phenomenon, not the force. 'Magnetic force' is too general, and the electric force is the opposing force of the Hall field that balances the Lorentz force in the steady state.

Q: What is the significance of the "quantum Hall effect" observed in graphene ?

The quantum Hall effect in graphene demonstrates the unique behavior of charge carriers in graphene.In 2005 graphene was found to show an unusual, 'half-integer' quantum Hall effect, with plateaus in Hall conductivity at \(4(n + 1/2)e^{2}/h\). This comes from its electrons behaving as massless Dirac fermions with a linear energy-momentum relation and a Berry phase of \(\pi\). In graphene the effect can even be seen at room temperature in strong fields.It does not indicate a bandgap; pristine graphene is gapless. It has nothing to do with thermal conductivity, which in graphene is in fact very high. And it is directly tied to graphene's electronic properties, so the last option is wrong.

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Directions : Q. Nos. 21 to 30 : The following items consist of two statements, one labelled the “Assertion (A)” and the other labelled the “Reason (R)”. You are to examine these two statements carefully and decide if the Assertion (A) and the Reason (R) are individually true and if so, whether the Reason is a correct explanation of the Assertion. Select your answers to these items using the codes given below and mark your answer accordingly.

Assertion (A) : If a semiconductor is placed in a transverse magnetic field B and an electric field E is applied across its other two faces, then it would produce an electric current I, in the direction perpendicular to both B and E.

Reason (R) : Hall co-efficient is proportional to the mobility of charge carrier in semi-conductor.

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 correct explanation of (A).
C.(A) is true, but (R) is false.
D.(A) is false, but (R) is true.

Exam Year(s)

UGC NET - 2012, UGC NET - 2014,

Answer: B

The keyed answer is that both statements are true but (R) is not the correct explanation of (A). In the Hall effect a transverse magnetic field and a current give an electric field, the Hall field, perpendicular to both, and the Hall coefficient is proportional to the mobility for a given conductivity, so both statements are accepted as true. The assertion, however, is about the direction of the effect, and the mobility dependence of the Hall coefficient does not explain it. Option A, which makes (R) the explanation, is therefore wrong, and options C and D call a true statement false.

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Force exerted by magnetic field in Hall effect transducer is :

A.Lorentz force
B.Hall effect
C.Magnetic force
D.Electric force

Exam Year(s)

MH SET - 2020, SET Exam - 2020,

Answer: A

The force is the Lorentz force.

In a Hall effect transducer, charge carriers moving through a conductor or semiconductor in a magnetic field experience the force F = q(v × B). This Lorentz force pushes them to one side of the material, building up the Hall voltage across it, which the transducer measures.

The Hall effect is the resulting phenomenon, not the force. 'Magnetic force' is too general, and the electric force is the opposing force of the Hall field that balances the Lorentz force in the steady state.

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What is the significance of the "quantum Hall effect" observed in graphene ?

A.It indicates the presence of a bandgap in graphene
B.It demonstrates the unique behavior of charge carriers in graphene
C.It signifies the low thermal conductivity of graphene
D.It is unrelated to the electronic properties of graphene

Exam Year(s)

MH SET - 2025, SET Exam - 2025,

Answer: B

The quantum Hall effect in graphene demonstrates the unique behavior of charge carriers in graphene.

In 2005 graphene was found to show an unusual, 'half-integer' quantum Hall effect, with plateaus in Hall conductivity at \(4(n + 1/2)e^{2}/h\). This comes from its electrons behaving as massless Dirac fermions with a linear energy-momentum relation and a Berry phase of \(\pi\). In graphene the effect can even be seen at room temperature in strong fields.

It does not indicate a bandgap; pristine graphene is gapless. It has nothing to do with thermal conductivity, which in graphene is in fact very high. And it is directly tied to graphene's electronic properties, so the last option is wrong.

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Hall effect can be used to measure

1. conductivity of the charge carrier.
2. mobility of the charge carrier.
3. the number of valence electrons per atom.
4. band gap of the material. Which of the following is correct ?

A.1 and 2 are true
B.2 and 3 are true
C.3 and 4 are true
D.1 and 4 are true

Exam Year(s)

UGC NET - 2013,

Answer: A

Statements 1 and 2 are true, which is option (A). The Hall coefficient gives the carrier concentration and its sign, and combined with the measured conductivity it gives the mobility, \(\mu = \sigma R_{H}\). So the conductivity and mobility of the carriers can be obtained from a Hall measurement. The number of valence electrons per atom (statement 3) is not what the effect measures directly, and the band gap (statement 4) is found from the temperature dependence of conductivity, not from the Hall voltage alone. That removes (B), (C) and (D).

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A transducer converts

1. A potential difference is developed across a current carrying metal strip when the strip is placed in transverse magnetic field.
2. The Hall effect is very weak in metals but large in semiconductors.
3. The Hall effect is very weak in semiconductors but is large in metals.
4. It is applied in the measurement of the magnetic field intensity.
Codes :

A.1, 2 & 3 only
B.2 & 4 only
C.1, 3 & 4 only
D.1, 2 & 4 only

Exam Year(s)

UGC NET - 2013,

Answer: D

This is the Hall effect: a potential difference appears across a current-carrying strip placed in a transverse magnetic field, so statement 1 is correct. The effect is small in metals, where the carrier density is huge, and large in semiconductors, where it is much smaller, so statement 2 is right and statement 3 is the reverse. Since the Hall voltage is proportional to the field, it is used to measure magnetic field intensity: statement 4 is correct. The answer is 1, 2 and 4.

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Hall Effect Questions and Answers

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Hall Effect Questions and Answers

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