Physics questions and answers

Physics Questions and Answers

If you want to learn more about the nature and properties of matter and energy or you're simply preparing for a Physics exam, these Physics past questions and answers are ideal for you.

21.

An electron moves from an energy level of -8.6 eV to another level of -3.5 eV. Determine the frequency of the absorbed radiation. [1 eV = 1.6 × \(10^{19}\) J, h = 6.6 × \(10^{34}\) Js]

A.

\( 2.93 \times 10^{15}\)Hz

B.

\( 3.59 \times 10^{16}\)Hz

C.

\( 5.39 \times 10^{15}\)Hz

D.

\( 1.24 \times 10^{15}\)Hz

Correct answer is D

h = \( 6.6 \times 10^{-34}\)Js, 1eV =  \( 1.6 \times 10^{-19}\)J, \(E_1\) = - 8.6eV, \(E_2\) = - 3.5eV, f = ?

ΔE = hf 

f = \(\frac{ΔE}{h}\)

ΔE =  \(E_2\) -  \(E_1\) = - 3.5eV - (- 8.6eV) = 5.1eV

but 5.1eV = 5.1 X \( 1.6 \times 10^{-19}\) = \( 8.16 \times 10^{-19}\)J

f =  \(\frac{8.16 \times 10^{-19}}{ 6.6 \times 10^{-34}}\)

Therefore, f =  \( 1.24 \times 10^{15}\)Hz

22.

The range of wavelengths of the infrared waves in an electromagnetic spectrum is \(10^{-3}\) m  to \(10^{-6}\)m. The wavelength of the radiation is

A.

longer than \(10^{-6} m\).

B.

shorter than \(10^{-6} m\).

C.

shorter than \(10^{3} m\).

D.

longer than \(10^{3} m\).

Correct answer is A

The range of wavelengths for infrared waves is given as \(10^{-3}\) m  to \(10^{-6}\)m. This means that the wavelength of the radiation is longer than \(10^{-6} m\) but shorter than \{10^{-3} m\). Therefore, the only correct option is that the wavelength is longer than \(10^{-6} m\).

23.

The ratio of maximum range to maximum height of a projectile is 4. Determine the angle of projection.

A.

\(30^0\)

B.

\(60^0\)

C.

\(45^0\)

D.

\(0^0\)

Correct answer is C

Maximum Range R = \(\frac{u^2sin2\theta}{g}\)

maximum height H = \(\frac{u^2sin^2\theta}{2g}\)

But R : H = 4

\(\frac{u^2sin2\theta}{g}\) :  \(\frac{u^2sin^2\theta}{2g}\) = 4

\(\frac{u^2sin2\theta}{g} \times\frac{2g}{u^2sin^2\theta}\) = 4

 \(\frac{2sin2\theta}{sin^2\theta}\) = 4 

since 2sinΘ = 2sinΘcosΘ

 \(\frac{2 \times 2sin\theta cos\theta}{sin^2\theta}\) = 4 

 \(\frac{4sin\theta cos\theta}{sin^2\theta}\) = 4 

\(\frac{sin\theta cos\theta}{sin^2\theta}\) = 1

\(\frac{cos\theta}{sin\theta}\) = 1

\(\frac{sin\theta}{cos\theta}\) = 1 

\(tan \theta\) = 1

\(\theta = tan^{-1}1\) = 45°

24.

A charge of 10 C is transferred across a potential difference of 220 V. Determine the work done.

A.

22J

B.

2200J

C.

210J

D.

230J

Correct answer is B

The work done in moving a charge across a potential difference is given by the formula W = QV, where W is the work done, Q is the charge and V is the potential difference. Substituting the given values, we get W = 10 C * 220 V = 2200 J. Hence, the work done is 2200 J.

25.

A sound of frequency 512 Hz reaches a listener 100 m away. If the sound travels in air at s.t.p., what is its wavelength?
[speed of sound in air = 331 m/s]

A.

1.550m

B.

0.646m

C.

5.120m

D.

0.195m

Correct answer is B

f = 512Hz, V = 331m/s    λ  = ?

V = f λ 

λ  = \(\frac{v}{f} = \frac{331}{512}\)

λ  = 0.646m.