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1. Magnets are made from alloys of iron, cobalt and nickel.

2. Nipermag is an alloy made up of iron, nickel, aluminium and titanium whereas alnico is an alloy made up of aluminium, nickel and cobalt.

1. A metal detector is an electronic instrument which detects the presence of metals nearby.

2. The function of these machines is based on electromagnets.

3. Metal detectors are useful for finding metal inclusions hidden within objects, or metal objects buried underground.

4. They often consist of a handheld unit with a sensor probe which can be swept over the ground or other objects.

5. Metal detectors in the food manufacturing industry are used to detect and eliminate threats of metal contaminants in food.

6. Metal detectors are used in very important places like an airport, bus station, temples, hospitals, railway stations, theaters, malls.

7. They are used for inspection of persons entering these places.

8. In geology, these machines are used to detect the presence and quantity of metals.

1. The earth is called as a gigantic magnet because north pole of a freely suspended magnet always settles in the direction of the geographic north pole of the earth.

2. It means that the South pole of some gigantic magnet must be near the geographic north pole of that magnet, near the geographic south pole of the earth.

3. Gilbert inferred from this that the earth itself is a gigantic magnet.

i. south pole

ii. A/M (Amperes per metre)

iii. barmagnet

iv. Michael Faraday

v. magnetic field

The north pole of a freely suspended magnet settles in the direction of the geographic north pole of the earth. It settles in north-south direction.

1. Freely suspended magnet does not point to north, but aligns to earth’s magnetic field axially ie – north-south.

2. The magnetic pole of the earth is different from true north (geographic north) because the magnetic north is constantly changing.

3. It leads to a margin of error called declination in which there is an angle of difference (11.51)° between Magnetic North and True North.

4. That is the reason the magnetic needle does not settle parallel to the ground.

North, all magnetic needle will show north direction.

1. A bar magnet kept on the cardboard arranges the iron fillings in line because of the ‘magnetic lines of force’.

2. These magnetic lines gauge the intensity of the bar magnet.

3. The intensity of the magnetic field is low where the lines of force are sparse and the intensity is high where the lines of force are concentrated.

4. Therefore, the iron fillings arrange themselves according to intensity of the magnetic lines of force.

Opposite magnet poles attract each other.

1. The magnetic force, is a consequence of the electromagnet force, one of the four fundamental forces of nature.

2. It occurs whenever objects interact in which there is charge in motion, eg. compass, a motor.

3. Magnetic force is an attraction or repulsion that arises between electrically charged particles because of their motion.

1. The region around the magnet where the magnetic force acts is known as the magnetic field.

2. It has its influence over a certain distance where these magnetic lines of force act.

3. As these pins are outside this area of influence, a bar magnet does not attract those pins which are at a distance.

The north pole of the spherical magnet will get attracted towards the south pole of the bar magnet.

Magnetic force acts without even direct contact because of the penetrating ability of the magnetic field.

A magnet can attract the opposite pole of the magnet as well as magnetic substances (iron, cobalt, nickel).

So if a magnet attracts another object, we cannot say that other object is a magnet or a magnetic substance.

But if the magnet repels the object then we can surely say that the other object is a magnet because like poles of magnets repel each other.

When a charge of IC, moving with velocity 1 m/s, normal to the magnetic field, experiences a force 1 N, the magnetic field is said to be one tesla.

The correct answer is (d) Li⁺⁺.

The correct answer is (a) (b) (d)

(a) E = 0,B = 0 

(b) E= 0, B ≠ 0 

(d) E ≠ 0, B ≠ 0.

(a) the electric field must be zero

(d) the magnetic field may or may not be zero.

Explanation:

Force on  charged particle in an electric eld, F = q E   ------(1) 

Force on charged particle in a magnetic eld F = q (v x B) = qvB sinθ    ---------(2) where boldface letter represent vector nature of that quantity, q is charge of the particle, v is the velocity of the particle( if any), and θ is the angle between velocity and magnetic eld. 

From (1) , F_E = 0 only when either q = 0 or E = 0. 

Let q≠0, and F ≠ 0, then we must have E ≠ 0 . 

From (2) , if q≠0, v≠0 and B≠0 even then F_B can be 'zero' because of  θ = 0⁰ or 180⁰

B = 0.20T, v = ? m = 0.010g = 10^–5kg, q = 1 × 10^-5C

Force due to magnetic field = Gravitational force of attraction

So, qvB = mg

=> 1 × 10^–5 × v × 2 × 10^–1 = 1 × 10^–5 × 9.8

=> v = (9.8 x 10^-5)/(2 x 10^-6) = 49m/s.

The correct answer is (b) E= 0, B ≠ 0

τ = ni vector A x vector B

=>  τ = ni ABsin90^º = => 0.2 = 100 x 2 x 5 x 4 x 10^-4 x B

=> B = 0.2/(100 x 2 x 5 x 4 x 10^-4) = 0.5Tesla
 

r = 0.5cm = 0.5 × 10^–2m

B = 0.4T, E = 200V/m

The path will straighten, if qE = quB => E = (rqB X B)/m  [∴ r = mv/qB]

=> E = rqB²/m => q/m = E/B²r = 200/(0.4 x 0.4 x 0.5 x 10^-2) = 2.5 x 10⁵c/kg

n = 500, r = 0.02m, θ = 30°

i = 1A, B = 4 × 10^–1T

i = μ × B = μB Sin30° = niABSin30°

= 500 × 1 × 3.14 × 4 × 10^–4 × 4 × 10^–1 × (1/2) = 12.56 × 10^–2 = 0.1256 ≈ 0.13N-M

n = 50, r = 0.02m

A = π × (0.02)², B = 0.02T

i = 5A, μ = niA = 50 × 5 × π × 4 × 10^–4

τ is max. when θ = 90°

τ = μ × B = μBSin90° = μB = 50× 5 × 3.14 × 4 × 10^–4 × 2 × 10^–1 = 6.28 × 10^–2N-M

Given τ = (1/2)τ_max

=> Sinθ = (1/2)

or, θ = 30° = Angle between area vector & magnetic field.

=> Angle between magnetic field and the plane of the coil = 90° – 30° = 60°

The correct answer is (d) Li⁺⁺.