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1. The current sensitibility of a moving coil galanometer increases with decrease in:

(a) magnetic field
(b) area of a coil
(c) number of turns
(d) None of these

2. The permeability of a paramagnetic substance is:

(a) very large
(b) small but more than unity
(c) less than unity
(d) negative

3. 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

4. What is the angle of dip at the magnetic poles?

(a) \(30^\circ\)
(b) \(0^\circ\)
(c) \(45^\circ\)
(d) None of these

5. 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

6. 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

7. When charged particle enters a uniform magnetic field, its K.E.:

(a) remains constant
(b) increases
(c) decreases
(d) becomes zero

8. 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

9. Isoclinic lines are the lines joining places with :

(a) equal dip
(b) equal declination
(c) equal dip and declination
(d) None of these

10. The most suitable metal for making permanent magnets is :

(a) iron
(b) steel
(c) copper
(d) aluminium

11. Earth’s magnetism was discovered by:

(a) Gauss
(b) Oersted
(c) Ampere
(d) Gilbert

12. 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

13. A current carrying circular loop of radius R is placed in the x-y plane with centre at the origin. Half of the loop with x > 0 is now bent so that it now lies in the y-z plane.

(a) The magnitude of magnetic moment now diminishes
(b) The magnetic moment does not change
(c) The magnitude of B at (0, 0, z), z > R increases
(d) The magnitude of B at (0, 0, z), z >> R is unchanged

14. An electron is projected with uniform velocity along the axis of a current carrying long solenoid. Which of the following is true?

(a) The electron will be accelerated along the axis
(b) The electron path will be circular about the axis
(c) The electron will experience a force at \(45^\circ\) to the axis and hence execute a helical path
(d) The electron will continue to move with uniform velocity along the axis of the solenoid

15. In a cyclotron, a charged particle

(a) undergoes acceleration all the time
(b) speeds up between the dees because of the magnetic field
(c) speeds up in a dees
(d) slows down within a dee and speeds up between dees

16. Assertion : Free electrons always keep on moving in a conductor even then no magnetic force act on them in magnetic field unless a current is passed through it.

Reason : The average velocity of free electron is zero.

(a) Assertion is correct, reason is correct; reason is a correct explanation for assertion
(b) Assertion is correct, reason is correct; reason is not a correct explanation for assertion
(c) Assertion is correct, reason is incorrect
(d) Assertion is incorrect, reason is correct

17. According to oersted, around a current carrying conductor, magnetic field exists

(a) as long as there is current in the wire
(b) even after removing the current in the wire
(c) only few seconds after removing the current
(d) None of these 

18. The magnetic field around a long straight current carrying wire is

(a) spherical symmetry
(b) cylindrical symmetry
(c) cubical symmetry
(d) unsymmetrical

19. If a copper rod carries a direct current, the magnetic field associated with the current will be

(a) only inside the rod
(b) only outside the rod
(c) both inside and outside the rod
(d) neither inside nor outside the rod

20. Magnetic field inside a solenoid is

(a) directly proportional to its length
(b) directly proportional to current
(c) inversely proportional to total number of turns
(d) inversely porportional to current

21. A long solenoid has a radius a and number of turns per unit length n. If it carries a current i, then the magnetic field on its axis is directly proportional to

(a) ani
(b) ni
(c) ni /a
(d) n2i

22. If a long hollow copper pipe carries a direct current, the magnetic field associated with the current will be

(a) only inside the pipe
(b) only outside the pipe
(c) neither inside nor outside the pipe
(d) both inside and outside the pipe

23. The unit of reduction factor of the tangent galvanometer is 

(a) Ampere
(b) Gauss
(c) Radian
(d) None of these

24. The resistance of an ideal voltmeter is 

(a) Zero
(b) Very low
(c) Very large
(d) Infinite

25. The direction of magnetic lines of forces close to a straight conductor carrying current will be :

(a) Along the length of the conductor
(b) Radially outward
(c) Circular in a plane perpendicular to the conductor
(d) Helical

Answer:

1. Answer : (d) None of these

Explanation: Sensitivity of a galvanometer increases when number of turns, area of coil and magnetic field increases whereas couple per unit twist decreases.

2.  Answer: (b) small but more than unity

Explanation: A paramagnetic material has a constant relative permeability slightly more than 1. When a paramagnetic material, such as platinum, is placed in a magnetic field, it becomes slightly magnetized in the direction of the external field. A ferromagnetic material, such as iron, does not have a constant relative permeability.

3. Answer: (c) Null points in the magnetic field of a bar magnet

Explanation: Null points exist where the field due to the magnet is equal and opposite to the horizontal component of the earth's field. Existence of null points in the magnetic field of a bar magnet shows that the earth behaves as a magnet.

4. Answer: (d) None of these

Explanation: At poles , \(\delta\) = 90^∘

5. Answer: (b) inversely proportional to the distance

Explanation: The strength of magnetic field around an infinite current carrying conductor is inversely proportional to the distance. In other words, if the distance between the magnetic field and the current is more, the strength of the field will be less. However if the distance is less, the strength is high.

6. Answer: (c) north to south

Explanation: The direction of magnetic field around a straight current carrying wire is given by the direction of curling of fingers of right hand when thumb points towards the direction of current. Hence, the magnetic field above the wire carrying current west to east is from north to south.

7. Answer: (a) remains constant

Explanation: When a charged particle enters a uniform magnetic field, its kinetic energy remains constant. The magnetic field always exerts a force perpendicular to the particle's velocity, so the magnitude of the velocity remains constant.

8. Answer: (a) high resistance in series with galvanometer

Explanation: Voltmeter is always connected in parallel to a circuit. Since Galvanometer is a very sensitive instrument, therefore it can not measure high potential difference. In order to convert a Galvanometer into voltmeter, a very high resistance known as "series resistance" is connected in series with the galvanometer.

9. Answer: (a) equal dip

Explanation: Isogonic lines join the points of equal declination, agonic lines pass through points of zero declination, isoclinic lines joins the points of equal dip or inclination, aclinic lines join the places of zero dip and isodynamic lines joins the places of same horizontal field.

10. Answer: (b) steel

Explanation: Steel is highly effective for this purpose because of the natural positioning of its atoms. Steel isn't the only material used to make permanent magnets. Permanent magnets are also made of ceramic, iron, cobalt, nickel, gadolinium and neodymium.

11. Answer: (d) Gilbert

Explanation: William Gilbert was the man who discovered the Earth's magnetic field.

12. Answer: (c) momentum of the particle

Explanation: q₀ BR = Mv 

i. e. R = Mv / Bq₀

13. Answer: (a) The magnitude of magnetic moment now diminishes

Explanation: For a circular loop of radius R carrying current I placed in x−y plane, the magnetic moment M =I x πR². It acts perpendicular to the loop i.e., along z-direction. When half of the current loop is bent in y−z plane, then magnetic moment due to half current loop in x−y plane, M₁=I(πR²/ 2) acting along z-direction. Magnetic moment due to half current loop in y−z plane, M₂ =I(πR²/2) along x -direction.

14. Answer: (d) The electron will continue to move with uniform velocity along the axis of the solenoid

Explanation: Magnetic field (\(\overset{-}{B}\) ) due to the current-carring solenoid is along its axis, i.e in the direction of unifrom velocity (\(\overset{-}{v}\)) the electron Clearly, as, the electfon continues to move with uniform velocity along the axis of the solenoid.

15. Answer: (a) undergoes acceleration all the time

Explanation: In a cyclotron, charged particle experiences coulombic force(force due to electric field) between the Dees and magnetic force ( force due to magnetic field ) while circulating inside the Dees. In total, it always experiences a force. 

16. Answer: (a) Assertion is correct, reason is correct; reason is a correct explanation for assertion

Explanation: In the absence of the electric current, the free electrons in a conductor are in a state of random motion, like molecule in a gas. Their average velocity is zero. i.e. they do not have any net velocity in a direction. As a result, there is no net magnetic force on the free electrons in the magnetic field. On passing the current, the free electrons acquire drift velocity in a definite direction, hence magnetic force acts on them, unless the field has no perpendicular component.

17. Answer: (a) as long as there is current in the wire

Explanation: According to oersted, around a current carrying conductor, magnetic field exists as long as there is current in the wire.

18. Answer: (b) cylindrical symmetry

Explanation: The magnetic field around a long straight current carrying wire is cylindrical symmetry.

19. Answer: (c) both inside and outside the rod 

Explanation: For solid rod, there will be current flowing inside the rod, so there will be magnetic field (Ampere circuital law). There will magnetic field outside the rod and it will decrease as we increase the distance.

20. Answer: (b) directly proportional to current

Explanation: Magnetic field inside a solenoid is given by

B = μ₀nI therefore, B \(\propto\) I

21. Answer: (b) ni

Explanation: The magnetic field due to a long solenoid is given by:

B = μ₀ni

⇒B\(\propto\)ni.

22. Answer: (b) only outside the pipe

Explanation: For a loop inside the hollow portion of the conductor, the current enclosed is zero until the loop is on the surface or inside the material of the conductor.
∴B_inside = 0 ∴B_inside = 0
For any loop outside, current enclosed by the amperian loop is not zero, hence magnetic field is non-zero.

23. Answer: (a) Ampere

Explanation: Reduction factor of a tangent galvanometer is equal to current, required to be passed through galvanometer to produce a deflection of 45^∘. Reduction factor is measured in ampere.

24. Answer: (d) Infinite

Explanation: A voltmeter is a device that is used to measure the potential difference between the two points in a circuit. The resistance of an ideal voltmeter is infinite.

25. Answer: (c) Circular in a plane perpendicular to the conductor

Explanation: The direction of magnetic lines of forces close to a straight conductor carrying current will be circular in a plane perpendicular to the conductor.

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