Question 11
(a) Explain briefly dielectric strength
(b) An electromagnetic wave has its wavelength shorter than those of radio wave and microwave but longer than that of visible light.
i. Identify the wave
ii. Name one suitable detector for the wave.
iii. Name one source of the wave.
(c) An oil drop carrying a charge of 1.0 x 10-19 C is found to remain at rest in a uniform electric field of intensity 1200 N C-1. Calculate the weight of the oil drop.
(d) An RLC series circuit consists of 100Ω resistor, 0.05 H inductor and a 25 μF capacitor. A 220 V, 50 Hz mains voltage is applied across the circuit. Calculate the:
i. Impedance
ii. Current (π = 3.14)
Observation
Part (a): Candidates performance was very poor. A few candidates got the right response for this question. Teachers should improve on this area.
Part (b): Candidates performance was fair. Many candidates got the infra-red wave but failed the detector and source of the wave.
Part (c): Performance was fair. Many candidates were able to calculate the weight of the oil drop using the formula W = qE. However, some got confused and used W = B/q.
Part (d): Performance was fair. Many candidates had issues with the last part due to the use of a wrong formula for I (i.e. I = V/R instead of I = V/Z).