Test: Moving Charges and Magnetism - 2 - CUET Humanities MCQ

Repulsion is a sure test of magnetism. Repulsion takes place only between two likes poles of a magnet, whereas attraction takes place between two unlike poles of a magnet and also between a magnet and a magnetic material. So, if a material attracts other material, we cannot be sure whether it is a magnet or not.

As the electron moves undeflected between the electric field and the magnetic field, so the resultant force on the electron is zero.
qE = qvB
v = E/B

r = mv/Bq
⇒ 
=  cm = 16 cm

If a direct current is sent through a helical wire coil, the sense of the current in the adjacent turns will be the same. We know that parallel currents attract each other, so the coil will tend to get shorter.

The force on the moving charge particle due to the magnetic field is:

So, the direction of the force experienced by a charged particle, moving with a velocity v in a uniform magnetic field B, is perpendicular to both the velocity of the charged particle and the direction of the magnetic field.

When an electron moves in a magnetic field in a direction perpendicular to the field, then its path will be circular as the force exerted by the magnetic field is perpendicular to both the magnetic field vector and the velocity vector. The necessary centripetal force is provided by the force due to the magnetic field.

Radius of path of electron r = mv/Bq 
m and q remain unchanged. (as r₁ = r)
So, 

The point x = +a lies along the line of the straight section PQ of the circuit. Hence, the magnetic field at point x = a is zero.

Force F on a wire of length l = iLB
Therefore, force per unit length of the wire = F/L = iB = 10^–4 × 10 = 10^–3 Nm^–1

The magnetic field at the centre of the coil is given by:

Magnetic field can be doubled by changing n to 2n and by keeping the current same.
Hence, the correct choice is (4).

If a charged particle is released from rest in a region of steady and uniform electric and magnetic fields, which are parallel to each other, then there is no force exerted by the magnetic field on the charged particle as initially, the charged particle is at rest and after that, the direction of the velocity of the charged particle is along the direction of the charged particle i.e. , where the force on the charged particle will be exerted by the electric field i.e. .
Direction of the force exerted by the electric field will be the same as that of electric field, if the charged particle is positive.
Direction of the force exerted by the electric field will be opposite to the electric field, if the charged particle is negative.

The charge passing per second through any point of the path is v times the charge of the electron, i.e. i = ev. If A is the area of the orbit, the magnetic moment is:
m = iA = evπr²
Hence, the correct choice is (1).

Induced magnetism is defined as the magnetism acquired by a magnetic material kept near a magnet, and it precedes attraction.

Magnetic moment M = Current x Area =  

Magnetic moment m = AI = πr²I, where r is the radius of the circular loop.
Now, the circumference of the circle = length of the wire, i.e.
2πr = L
or r² = 
Therefore, m = r²I = 
Hence the correct choice is (4)