WAEC Physics Past Questions & Answers - Page 118

586.

An ammeter connected to an a.c circuit records 5.5. The peak current in the circuit is

A.

7.8A

B.

7.1A

C.

3.8A

D.

3.5A

Correct answer is A

\(I_o = I_{rms} \times \sqrt{2} = 5.5 \times 1.41 = 7.8A\)

587.

An inductor of inductance 1.0H is connected in series with a capacitor of capacitance 2.0\(\mu F\) in an a.c. circuit. to resonate

A.

112.5Hz

B.

225.0Hz

C.

323.5Hz

D.

707.1Hz

Correct answer is A

fo = \(\frac{1}{2 \pi \sqrt{LC}} = \frac{1}{2 \times 3.14 \sqrt{1 \times 2 \times 10^{-6}}}\)

= 112.5Hz

588.

If the direction of the curent in a straight wire is reversed, the magnetic field

A.

remains the same

B.

becomes parallel to the wire

C.

ceases to exist

D.

is oppositely directed

Correct answer is D

No explanation has been provided for this answer.

589.
590.

A wire of resistivity 4.40 x 10-5\(\Omega\) cm has a cross sectional area of 7.50 x 10-4 cm2. Calculate the length of the wire that will be required to make a 4.0\(\Omega\) resistor

A.

82.50 cm

B.

68.18cm

C.

15.90cm

D.

11.95cm

Correct answer is B

L = \(\frac{R.A}{e} = \frac{4 \times 7.50 \times 106{-4}}{4.40 \times 10^{-5}} = 68.18cm\)