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NCERT Solutions for class 12 Physics | Chapter 4 - Moving Charges and Magnetism

Questions
1 The radius of the trajectory of a charged particle in a uniform magnetic field is proportional to the:
A charge on the particle
B energy of the particle
C momentum of the particle
D all the above

Answer:momentum of the particle
2 10 eV electron is circulating in a plane at right angle to a uniform field of magnetic induction 10-1 Wb/m² (1G). The orbital radius of electron is:
A 12 cm
B 16 cm
C 11 cm
D 18 cm

Answer:11 cm
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3 Earth’s magnetism was discovered by:
A Gauss
B Oersted
C Ampere
D Gilbert

Answer:Gilbert
4 Isoclinic lines are the lines joining places with :
A equal dip
B equal declination
C equal dip and declination
D None of these

Answer:equal dip
5 When charged particle enters-a uniform magnetic field, its K.E.:
A remains constant
B increases
C decreases
D becomes zero

Answer:remains constant
6 Which of the following is not a unit of magnetic induction?
A gauss
B tesla
C oersted
D weber/metre²

Answer:oersted
7 A current carrying power line carries current from west to east. Then the direction of the magnetic field 2 m above it is :
A west to east
B south to north
C north to south
D None of these

Answer:north to south
8 What happens to the magnetic field at the centre of a circular current carrying coil if we double the radius of the coil keeping the current unchanged?
A halved
B doubled
C quadrupled
D remains unchanged

Answer:halved
9 What is the angle of dip at the magnetic poles ?
A 30°
B 0°
C 45°
D None of these

Answer:None of these
10 A wire of length 2 metre carries a current 1 ampere, is bent to form a circle. The magnetic moment of the coil is :
A 2π
B π/2
C π/4
D 1/π

Answer:1/π
11 The force between two parallel current carrying conductors is F. If the current in each conductor is doubled, then the force between them becomes :
A 4F
B 2F
C F
D F/4

Answer:4F
12 The strength of the magnetic field around an infinite current carrying conductor is :
A same everywhere
B inversely proportional to the distance
C directly proportional to the distance
D None of these

Answer:inversely proportional to the distance
13 To convert galvanometer into voltmeter one should connect :
A high resistance in series with galvanometer
B low resistance in series with galvanometer
C high resistance in parallel with galvanometer
D low resistance in parallel with galvanometer

Answer:high resistance in series with galvanometer
14 The magnetic field of a given length of a ware for single turn coil at its centre is B. Then.its value for two turns of coil will be :
A B/4
B B/2
C 4B
D 2B

Answer:4B
15 The magnetic field produced by an / meter long straight (x cry thin) current (I) carry ing conductor at any point on itself is :
A zero
B infinite
C µ0l/4πl
D µ0l/2πl

Answer:zero
16 When we double the radius of a coil keeping the current through it unchanged, what happens to the magnetic field directed along its axis at far off points?
A halved
B doubled
C quadrupled
D remains unchanged

Answer:remains unchanged
17 According to Gauss’s theorem in magnetism, surface integral of magnetic field intensity over a surface (closed or open) is always:
A -1
B 1
C 0
D infinity

Answer:0
18 The sensitivity of a tangent galvanometer can be increased by increasing:
A the radius of the coil
B the external magnetic field
C the number of turns of the coil
D all the above

Answer:the external magnetic field
19 Which of the following shows that the earth behaves as a magnet?
A Repulsion between like poles .
B Attraction between unlike poles
C Null points in the magnetic field of a bar magnet
D No existence of isolated magnetic poles

Answer:Null points in the magnetic field of a bar magnet
20 Circular loop of radius 0.0157 m carries a current 2 A. The magnetic field at the centre of the loop is :
A 1.57 × 10-3Wb/m²
B 8.0 × 10-5 Wb/m²
C 2.0 × 10-3 Wb/m²
D 3.l4 × 10-1 Wb/m²

Answer:8.0 × 10-5 Wb/m²

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