# C.3 Wave phenomena SL Paper 2- IBDP Physics 2025- Exam Style Questions

IBDP Physics SL 2025 -C.3 Wave phenomena SL Paper 1 Exam Style Questions

## Topic: C.3 Wave model  SL Paper 1

Wavefronts, Rays, Reflection, Refraction, Diffraction, Shell’s Law, Wave Superposition, Two-Source Interference

### Question-C.3 Wave phenomena SL Paper 2

A group of students perform an experiment to find the refractive index of a glass block. They measure various values of the angle of incidence $$i$$ and angle of refraction $$r$$ for a ray entering the glass from air. They plot a graph of the $$\sin r$$ against $$\sin i$$.

They determine the gradient of the graph to be $$m$$.
Which of the following gives the critical angle of the glass?

A. $$\sin ^{-1}(m)$$

B. $$\sin ^{-1}\left(\frac{1}{m}\right)$$

C. $$m$$

D. $$\frac{1}{m}$$

Ans:A

\begin{aligned} \quad & n_1 \text { sin i }=n_2 \sin r \\ & \text { Snalls Law. } \\ m(slope) = & \frac{\sin r}{\sin i}=\frac{n_1}{n_2}=\frac{1}{n}\end{aligned}

$n_1=1$ and $n_2 =n$

Now , TIR comes to action from which we have to calculate the critical angle (and happens only when ray goes from denser to rarer medium)

\begin{aligned} & n \cdot \sin \theta_c=1 \cdot \sin 90 \\ & n \cdot \sin \theta_c=1 \Rightarrow \theta_c=\sin ^{-1}\left(\frac{1}{n}\right)\\ &\theta_c=sin ^{-1} m \end{aligned}

### Question

Two identical sources oscillate in phase and produce constructive interference at a point $$P$$. The intensity recorded at $$\mathrm{P}$$ is $$I$$.
What is the intensity at $$P$$ from one source?

A. $$\sqrt{2} I$$

B. $$I$$

C. $$\frac{I}{2}$$

D. $$\frac{I}{4}$$

Ans:D

When two identical sources oscillate in phase and produce constructive interference at a point, the resulting intensity at that point is four times the intensity from one of the sources.

So, the intensity at point P from one source is:D. $$\frac{I}{4}$$

Question

Electromagnetic waves

A.     always obey an inverse square law.

B.     are made up of electric and magnetic fields of constant amplitude.

C.     always travel at the same speed in a vacuum.

D.     are always polarized.

### Markscheme

C

In physics, electromagnetic radiation consists of waves of the electromagnetic field, which propagate through space and carry electromagnetic radiant energy. It includes radio waves, microwaves, infrared, light, ultraviolet, X-rays, and gamma rays. All of these waves form part of the electromagnetic spectrum.

Electromagnetic radiation is a type of energy that is commonly known as light. Generally speaking, we say that light travels in waves, and all electromagnetic radiation travels at the same speed which is about $$3.0\times 10^{-8}$$ meters per second through a vacuum.

Question

Waves emitted from sources X and Y have equal wavelengths and are initially in phase. The waves interfere destructively at point P, where the path difference is 0.60m.

What is a possible value for the wavelength of the waves?

A. 0.20 m
B. 0.30 m
C. 0.40 m
D. 0.60 m

### Markscheme

C

For destructive interference,
Path difference$$=(2n+1)\frac{\lambda}{2}$$
$$0.6=(2n+1)\frac{\lambda}{2}$$

for possible values of $$\lambda$$  we have check for different values of n.

For , n=0

$$0.6=\frac{\lambda}{2}$$
$$\lambda=1.2$$  not in gievn option

For n=1
$$0.6=(2\times1+1)\frac{\lambda}{2}$$
$$\lambda=0.4$$   option-B

### 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?