Electricity and Magnetism Answers

a. A transformer is used to change the 230 volt mains electricity supply to the 12 volts

needed to operate a low voltage halogen lamp. The current through the halogen lamp

is 4 amps. Assuming that the transformer is 100 % efficient determine the:

ii. number of turns on the primary coil if there are 200 turns on the secondary.

iii. power output of the transformer.

b. A metallic conductor of length 0.40m carrying a current of 5 A experiences a 

Force of 26N in a magnetic field of strength 15 T. Determine the angle between 

the current in the conductor and the magnetic field. 

a) An electron moving at 5 x 10³ m/s in a 1.5T magnetic field experiences a magnetic force of 1.6× 10⁻¹⁶N. What angle does the velocity of the electron make with the magnetic field? 

b) A cosmic ray proton moving toward the earth at 5 x 10⁷ m/s experiences a magnetic force of 1.70 × 10 ⁻¹⁶N. What is the strength of the magnetic field if there is a 45° angle between it and the proton’s velocity? 

If the back EMF induced in a coil when current changes from 1 ampere to 0 in 1 millisecond, is 5 volts, the self inductance of the coil is:-

(A) 5H

(B) 1H

(C) 5×10^-3 H

(D) 5×10^3 H

Three charges, +5Q, -5Q, and +3Q are located on the y-axis at y = +4a, y = 0, and y=-4a , respectively. The point P is on the x-axis at x = 3a. (a) How much energy did it take to assemble these charges? (b) What are the x, y, and 2 components of the electric field Ę at P? (c) What is the electric potential V at point P, taking V = 0 at infinity? (d) A fourth charge of +Q is brought to P from infinity. What are the x, y, and z components of the force F that is exerted on it by the other three charges? (e) How much work was done (by the external agent) in moving the fourth charge +Q from infinity to P?

explain what is meant by the statement that electrostatic forces obey the principle of superposition

Calculate the equivalent resistance for the circuit which is connected to 24V battery and also find the potential difference across 4ohms and 6ohms resistors in the circuit.

The electric potential difference between the ground and a cloud in a particular 

thunderstorm is 1.2X10^9 V. In the unit of electron- volt, what is the magnitude of the 

electric potential energy of an electron that moves between ground and the clouds?

Three +0.12C charges from an equilateral triangle 1.7m on a side. Using energy supplied

At the rate of 0.83KW, how many days would be required to move one of the charges to

the midpoint of the line joining the other two charges?

Can megnetic fields exist independently of electric charges? 

1. An infinite non-conducting sheet has a surface charge density 𝜎 = 0.10𝜇𝐶/𝑚2 on one 

side. How far apart are equipotential surfaces whose potentials differ by 50Volts?

2. As a space shuttle moves through the dilute ionized gas of Earth’s ionosphere, the shuttle’s 

potentials is typically changed by -1.0V during one revolution. Assuming the shuttle is a 

sphere of radius 10m, estimate the amount of charge to collects.

3. What are the charge and the charge density on the surface of a conducting sphere of 

radius 0.15m whose potential is 200V with V=0 at infinity?

4. A spherical drop of water carrying a charge of 30pC has a potential of 500V at its surface 

(with V=0 at infinity). (a) What is the radius of the drop? (b) If two such drops of the same 

charge and radius combine to form a single spherical drop. What is the potential at the 

surface of the new drop?