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.
∴Binside = 0 ∴Binside = 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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