WAEC Physics Past Questions & Answers - Page 297

1,481.

If the frequency of the ac. circuit illustrated above is 500/π Hz what would be the reactance in the circuit? 

(Inductance (L) = 0.9H, Capacitance (C) = \(2 \times 10^{-6}\)

A.

0.0009Ω/π

B.

100Ω

C.

1030Ω

D.

400Ω

E.

2500Ω

Correct answer is D

Given Data: Frequency (F) = \(\frac{500}{π}\) , Inductance (L) = 0.9H, Capacitance (C) = \(2 \times 10^{-6}\)

Total circuit reactance = Inductive reactance ( X\(_L\) ) - Capacitive reactance ( X\(_C\) )

when  ( X\(_L\) ) >  ( X\(_C\) )

Inductive reactance ( X\(_L\) ) = 2πFL = 2 \(\times\) π \(\times\) \(\frac{500}{π}\) \(\times\) 0.9 = 900Ω

Capacitive reactance ( X\(_C\) ) = \(\frac{1}{2πFC}\) = \(\frac{1}{2 \times π \times 500/π \times 2 \times 10^{-6}}\)

= \(\frac{1}{2 \times 10^{-3}}\) = \(\frac{1}{0.002}\)  

= 500Ω

 

Total circuit reactance =  ( X\(_L\) ) -  ( X\(_C\) ) = (900 - 500)Ω

=400Ω

1,482.

A charge of 1.0 x 10-5 Coulombs experience force of 40N at a certain point in space. What is the electric field intensity?

A.

8.00 x 106NC-1

B.

4.00 x 106NC-1

C.

4.00 x 10-4NC-1

D.

2.00 x 10-4NC-1

E.

2.50 x 10-1NC-1

Correct answer is B

F = qE; E = F/q = 40/(1.0 x 10-5) = 4.0 x 106

1,483.

What is the value of R when G shows no deflection in the circuit illustrated above?

A.

80Ω

B.

75Ω

C.

45Ω

D.

20Ω

E.

10Ω

Correct answer is D

R/30 = 100/150R = 20Ω

1,484.

A work of 30 joules is done is transferring 5 millicoulombs of charge from a point B to a point A in an electric Held. The potential difference between B and A is

A.

1.7 x 10-4V

B.

3.4x10-4V

C.

1.5x10-1V

D.

6.0 x103V

E.

1.2 x104V

Correct answer is D

No explanation has been provided for this answer.

1,485.

What is the electric potential energy between two protons each of charge q and at a distance of r apart? (Permittivity of free space = εo)

A.

4πεoq2r

B.

qr/4πεo

C.

q/4πεor

D.

q2/4πεor

E.

q2/4πεo

Correct answer is C

No explanation has been provided for this answer.