# IB DP Physics 4.4 – Wave behavior: IB style Question Bank – SL Paper 1

### Question

Three quantities used to describe a light wave are

1. frequency

2. wavelength

3. speed.

Which quantities increase when the light wave passes from water to air?

A I and II only

B I and III only

C II and III only

D I, II and III

Ans: C

REFRACTIVE INDEX OF SECOND MEDIUM W.R.T. FIRST MEDIUM
Now Refractive Index of Water is more than Air , hence Velocity of light wave will be more in Air than Water.
Also Velocity and wavelength is related as
vp = nλ Where vp = Wave Velocity , n= Frequency and λ = Wavelength of Wave
Frequency is the characteristic of the source while wavelength is the characteristic of the medium. when monochromatic light travels from one medium to another its speed changes so its wavelength changes but frequency v remains unchanged.
Hence as velocity increases Wavelength will also increase

### Question

What are the changes in the speed and in the wavelength of monochromatic light when the light passes from water to air?

### Markscheme

A

REFRACTIVE INDEX OF SECOND MEDIUM W.R.T. FIRST MEDIUM
Now Refractive Index of Water is more than Air , hence Velocity of light wave will be more in Air than Water.
Also Velocity and wavelength is related as
vp = nλ Where vp = Wave Velocity , n= Frequency and λ = Wavelength of Wave
Frequency is the characteristic of the source while wavelength is the characteristic of the medium. when monochromatic light travels from one medium to another its speed changes so its wavelength changes but frequency v remains unchanged.
Hence as velocity increases Wavelength will also increase

### Question

A pair of slits in a double slit experiment are illuminated with monochromatic light of wavelength 480 nm. The slits are separated by 1.0 mm. What is the separation of the fringes when observed at a distance of 2.0 m from the slits?

A. 2.4 × 10–4 mm

B. 9.6 × 10–4 mm

C. 2.4 × 10–1 mm

D. 9.6 × 10–1 mm

### Markscheme

D

$$\beta =\frac{\lambda D}{d}$$
$$=\frac{480\times 10^{-9} \times 2}{10^{-3}}$$
$$=9.6\times 10^{-4}=9.6\times 10^{-1} mm$$

### Question

The diagram shows an interference pattern produced by two sources that oscillate on the surface of a liquid.

Which of the distances shown in the diagram corresponds to one fringe width of the interference pattern?

### Markscheme

C

Fringe width is the distance between two consecutive bright spots (maximas, where constructive interference take place) or two consecutive dark spots (minimas, where destructive interference take place).

### Question

The refractive index for light travelling from medium X to medium Y is $$\frac{4}{3}$$. The refractive index for light travelling from medium Y to medium Z is $$\frac{3}{5}$$. What is the refractive index for light travelling from medium X to medium Z?

A. $$\frac{4}{5}$$

B. $$\frac{15}{12}$$

C. $$\frac{5}{4}$$

D. $$\frac{29}{15}$$

### Markscheme

A

$$^X\mu _Y =\frac{\mu_Y}{\mu_X}=\frac{4}{3}$$
$$^Y\mu _Z =\frac{\mu_Z}{\mu_Y}=\frac{3}{5}$$
$$^X\mu _Z =\frac{\mu_Z}{\mu_X}=\frac{\mu_Y}{\mu_X} \times \frac{\mu_Z}{\mu_Y} =\frac{4}{3} \times \frac{3}{5} =\frac{4}{5}$$

### Question

When a sound wave travels from a region of hot air to a region of cold air, it refracts as shown.

What changes occur in the frequency and wavelength of the sound as it passes from the hot air to the cold air?

### Markscheme

B

Refractive index and Velocity is related as
Also
We have  $$\frac{\mu_{hot}}{\mu_{cold}}=\frac{sin\;i}{sin\;r}$$
now $$i> r$$ hence $$\mu_{cold}>\mu_{hot}$$
hence
$$v_{cold} <v_{hot}$$ or $$\lambda_{cold}<\lambda_{hot}$$ as $$v=f\lambda$$
Velocity decreases
Frequency does not depend on medium