Physics Questions & Answers - Free Online Practice

101.

The number of holes in an intrinsic semiconductor

is not equal to the number of free electrons

is greater than the number of free electrons

is equal to the number of free electrons

is less than the number of free electrons

Correct answer is C

An intrinsic semiconductor, also called an undoped semiconductor, is a pure semiconductor. In intrinsic semiconductors the number of excited electrons and the number of holes are equal: n = p

102.

The half life of a radioactive material is 12 days. Calculate the decay constant.

0.8663 $day^{-1}$

0.04331 $day^{-1}$

0.17325 $day^{-1}$

0.05775 $day^{-1}$

View answer & explanation

Correct answer is D

$T_ {^1/_2}$ = 12 days ;V=?

$T_ {^1/_2}$ = $\frac{0.693}{γ}$

⇒γ ⇒ $\frac{0.693}{t_{^1/_2}}$

⇒γ = $\frac{0.693}{12}$

⇒γ= 0.05775 $day^{-1}$

103.

A lorry accelerates uniformly in a straight line with acceleration of $4ms^-2$ and covers a distance of 250 m in a time interval of 10 s. How far will it travel in the next 10 s?

650

900

800

250

View answer & explanation

Correct answer is A

We first find the lorry's initial velocity

a = $4ms^-2$ , s= 250m, t= 10, u=?

⇒ ut + $\frac{1}{2}×4×(10^2) ⇒250= 10u + 200 ⇒ 250-200 = 10u ⇒ 50 = 10u ⇒U =\frac{50}{10}$ = $5ms^-1$

For the next 10s, we set t=20s

= s = (5 × 20) + $\frac{1}{2}×4×{20^2}$

= s = 100 + 800

⇒ 900 m

;Distance covered:900-250 =650m

104.

The terminals of a battery of emf 24.0 V and internal resistance of 1.0 Ω is connected to an external resistor 5.0 Ω. Find the terminal p.d.

18.0V

12.0V

16.0V

20.0V

View answer & explanation

Correct answer is D

ε = 24.0 V, r=1Ω, R=5.0Ω

terminal p·d = ?

ε = IR+Ir = I(R+r)

⇒ IR+Ir = I(R+r)

⇒ I = $\frac{24}{5+1}$

⇒ I = $\frac{24}{6}$

⇒ I = 4 A

terminal p·d = 4 × 5

terminal p·d = 20.0 V