WAEC Physics Past Questions & Answers - Page 99

491.

For photoelectric emission, the threshold frequency is the

A.

maximum frequency of incident radiation that will eject electrons

B.

minimum fraquency of incident radiation required to eject electrons

C.

frequency which results in the emission of the greater number of electrons

D.

fraquency whch impacts greatest kinetic energy to emitted electrons

Correct answer is B

No explanation has been provided for this answer.

492.

Which of the following practices will lead to losses in electrical power transmission?

A.

using transmission cables of large diameter

B.

transmitting at high voltage and low current

C.

transmitting at relatively low voltage and high current

D.

using a set-up transformer at the production end

Correct answer is C

No explanation has been provided for this answer.

494.

The resistivity, \(\mathit{P}\), of a material of length l, cross-sectional area A, resistance R, is given by the equation

A.

\(\mathit{P} = \frac{RA}{l}\)

B.

\(\mathit{P} = \frac{l}{RA}\)

C.

\(\mathit{P} = \frac{Rl}{A}\)

D.

\(\mathit{P} = \frac{R}{Al}\)

Correct answer is A

 resistivity P  is directly proportional to the product of resistance and cross-sectional area and inversely proportional to the length of the wire

495.

An ammeter with a full scale deflection of 10mA has an internal resistance 0.5\(\Omega\). calculate the resistance of the shunt required to adapt it to read up to 3A

A.

0.0167\(\Omega\)

B.

0.0130\(\Omega\)

C.

0.0250\(\Omega\)

D.

0.1000\(\Omega\)

Correct answer is A

\(R_2 = \frac{I_1R_1}{I_2} = \frac{0.01 \times 5}{2.99}\)

= 0.0167