JAMB Physics Past Questions & Answers - Page 154

766.

A conductor has a diameter of 1.00mm and length of 2.00m. If the resistance of the material is 0.1Ω, the resistivity is

A.

2.55 * 105 Ωm

B.

2.55 * 103 Ωm

C.

3.93 * 10-6 Ωm

D.

3.93 * 10-8 Ωm

Correct answer is D

\( R = \frac{1}{a} p \implies p = \frac{R.a}{1} = \frac{0.1 \times 3.14}{2} \left ( \frac{10^{-3}}{2} \right)^2 \\

\text{Therefore } p = \frac{0.1 \times 3.14 \times 10^{-6}}{2 \times 4} \\

= 0.3925 \times 10^{-7} \text{ OR } -3.930 \times 10 ^{-8}Ωm \)

767.

If two charged plates are maintained at a potential difference of 3 kv, the work done in taking a charge of 600µc across the field is

A.

0.8j

B.

1.8j

C.

9.0j

D.

18.0j

Correct answer is B

Workdone = product of the charge Q, and the p.d V.

i.e Work done = QV
= 600 * 10-6 *2.1 * 103

=1.8j

768.

The difference observed in solids, liquids and gases can be accounted for by

A.

The different molecules in each of them

B.

The spaces and forces acting between the molecules

C.

Their melting points

D.

Their relative masses

Correct answer is B

No explanation has been provided for this answer.

769.

Which of the following gas laws is equivalent to the work done?

A.

Boyle's law

B.

Charles law

C.

Pressure law

D.

van der Waal's law

Correct answer is A

Mathematically Boyle's law = PV = K
Where P = Pressure
and V = Volume


By definition Pressure = \( \frac{F}{A} = \frac{F}{M \times M} \)

Again Workdone = force x displacement

therefore \( PV = \frac{F}{A} \times V = \frac{F}{M^2} \times \frac{M^3}{1} \\

PV = \frac{F}{x\times x} \times \frac{x \times x \times x}{1} = F \times x \)

= force x displacement

770.

A string of length 4m is extended by 0.02m when a load of 0.4kg is suspended at its end. What will be the length of the string when the applied force is 15N?

A.

4.05m

B.

4.08m

C.

5.05m

D.

6.08m

Correct answer is B

from hooke's law F=Ke
\(
\frac{F_1}{e_1} - \frac{F_2}{e_2} \text{therefore}

\frac{4}{0.02} = \frac{15}{e_2} \)

e1 = \( \frac{0.02 x 15}{4} = 0.075M \)

The new length of the string is 4 + 0.075
= 4.075
= 4.08