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JAMB Physics Past Questions & Answers - Page 216

1,076.

Which of the following statements is CORRECT?

i. the mass number is equal to the total number of protons and electrons in an atom.
ii. the atomic number is equal to the number of protons in an atom.
iii. the number of electrons in an atom is equal to the total number of protons and neutrons in the nucleus.

i only

ii only

iii only

i and ii only

ii and iii only

View answer & explanation

Correct answer is B

No explanation has been provided for this answer.

1,077.

The total length of a spring when a mass of 20g is hung from its end is 14cm, while its total length is 16cm when a mass of 30g is hung from the same end. Calculate the unstretched length of the spring assuming Hooke's law is obeyed.

9.33cm

10.00cm

10.66cm

12.00cm

15.00cm

View answer & explanation

Correct answer is B

Let unstretched length = L

e₁ = 14 - L and e₂ = 16 - L

Using, $\frac{m_1}{e_1}$ = $\frac{m_2}{e_2}$

$\frac{20}{14 - L}$ = $\frac{30}{16 - L}$

L = 10cm

1,078.

1,000 identical drops of oil of density 500kgm^-3 have a total mass of 5 x 10^-4kg. One of the drops forms a thin film of area 0.5m² on water. The thickness of the film is

2 x 10^-8m

2 x 10^-9m

2 x 10^-7m

3 x 10^-9m

2.8 x 10^-8m

View answer & explanation

Correct answer is B

Mass of one oil = $\frac{5 \times 10^{-4}}{1000}$

= 5 x 10^-4kg

Density = $\frac{\text {mass}}{\text{area x thickness}}$

500 = $\frac{5 \times 10^{-7}}{\text{0.5 x thickness}}$

thickness = 2 x 10^-9m