Quiz on Electrons

The cathode rays are the beam of,

• Protons

• Alpha rays

• Electrons

• Hydrogen

Answer explanation

The cathode rays are streams of electrons, which are negatively charged particles. They are produced in vacuum tubes and are distinct from protons, alpha rays, and hydrogen, making 'Electrons' the correct answer.

At what angle of incidence of a charge particle in magnetic field, the force on election is maximum?

• 0°

• 45°

• 90°

• 450°

Answer explanation

The force on a charged particle in a magnetic field is given by F = qvB sin(θ). This force is maximum when sin(θ) is maximum, which occurs at θ = 90°. Thus, the correct answer is 90°.

Which condition is essential during the measurement of velocity of oil drop in Millikan's experiment?

• Acceleration motion

• Decelerating motion

• Terminal velocity

• All above conditions

Answer explanation

In Millikan's experiment, the oil drop must reach terminal velocity for accurate velocity measurement. Both accelerating and decelerating motions occur during the process, making 'All above conditions' essential for precise results.

The specific charge of an electron is approximately;

• 1.8×10-11Ckg-1

• 1.8×1011Ckg-1

• 8.1×10-11Ckg-1

• 8.1×1011Ckg-1

Answer explanation

The specific charge of an electron is defined as its charge divided by its mass. The correct value is approximately 1.8×10^-11 C/kg, making the first option the correct answer.

A cathode ray tube has potential difference of V volts between the cathode and anode. Then, the speed (v) of cathode rays is given by,

• v ∝ 1V

• v ∝ V

• v ∝ V2

• v ∝ V

Answer explanation

The speed of cathode rays is directly proportional to the potential difference (V) between the cathode and anode. Thus, as V increases, the speed (v) of the cathode rays also increases, leading to the correct choice: v ∝ V.

A proton and an alpha particle are injected into a uniform magnetic field at right angles to the direction of field with equal linear momentum. Then, radii of their circular paths will be,

• 1:1

• 2:1

• 2:1

• 1:2

Answer explanation

The radius of the circular path in a magnetic field is given by r = p/(qB), where p is momentum, q is charge, and B is magnetic field strength. Since both particles have equal momentum and are in the same field, their radii are equal, hence 1:1.

Doubly ionized helium atom and a hydrogen ion are accelerated from rest through the same potential difference. The ratio of their final velocities will be,

• 1: 2

• 2:1

• 2:1

• 1:2

Answer explanation

The kinetic energy gained by each ion is equal to the work done by the electric field, given by qV. For He++ (charge 2e) and H+ (charge e), their final velocities v are related by v = sqrt(2qV/m). Thus, v(He++)/v(H+) = sqrt(2/1) = 2:1.

A particle with a specific charge S is fired with a speed v towards the wall. What minimum magnetic field must exist in this region for particle not to hit the wall?

• vsd

• 2vSd

• v2Sd

• v4Sd

Answer explanation

To prevent the particle from hitting the wall, the magnetic force must equal the centripetal force. The minimum magnetic field B is given by B = (mv)/(qv) = (m/q) * v, leading to B = vsd, where S is the charge.

The ratio of specific charge of a proton to that of a ∝-particle is:

• 4:1

• 1:2

• 1:4

• 2:1

Answer explanation

The specific charge is defined as charge per unit mass. A proton has a charge of +1e and a mass of approximately 1 u, while an alpha particle (2 protons + 2 neutrons) has a charge of +2e and a mass of about 4 u. Thus, the ratio is 4:1.

An electron enter in magnetic field with velocity 2×106ms-1 perpendicular to the field of 2×10-5T. What is the radius of the path of electron?

• 0.57m

• 7.5m

• 2.4m

• 0.24m

Answer explanation

The radius of the path of an electron in a magnetic field is given by r = mv/qB. Here, m = 9.11×10^-31 kg, v = 2×10^6 m/s, q = 1.6×10^-19 C, and B = 2×10^-5 T. Calculating gives r ≈ 0.57 m, which is the correct answer.