IB Physics Wave phenomena Practice Questions

Q: Snell's law for refraction at a boundary between two media is:

$n_{1}\sin\theta_{1}=n_{2}\sin\theta_{2}$. Snell's law: $n_{1}\sin\theta_{1}=n_{2}\sin\theta_{2}$, relating refractive indices and angles to the normal.

Q: Light passes from glass ($n=1.5$) toward air. Total internal reflection occurs when the angle of incidence exceeds the critical angle $\theta_{c}$, where:

$\sin\theta_{c}=\frac{1}{1.5}$. At the critical angle the refracted ray grazes the surface ($\theta_{2}=90^{\circ}$): $\sin\theta_{c}=\frac{1}{n}=\frac{1}{1.5}$.

Question 1

When a wave reflects from a plane surface, the angle of incidence equals the:

Accepted Answer

Angle of reflection. The law of reflection states the angle of incidence equals the angle of reflection, both measured from the normal.

Question 2

Snell's law for refraction at a boundary between two media is:

Accepted Answer

$n_{1}\sin	heta_{1}=n_{2}\sin	heta_{2}$. Snell's law: $n_{1}\sin	heta_{1}=n_{2}\sin	heta_{2}$, relating refractive indices and angles to the normal.

Question 3

The spreading of waves as they pass through a gap or around an obstacle is called:

Accepted Answer

Diffraction. Diffraction is the spreading of waves; it is most pronounced when the gap size is comparable to the wavelength.

Question 4

In a two-source interference pattern, constructive interference occurs where the path difference is:

Accepted Answer

A whole number of wavelengths. Constructive interference requires a path difference of a whole number of wavelengths: $n\lambda$.

Question 5

Light passes from glass ($n=1.5$) toward air. Total internal reflection occurs when the angle of incidence exceeds the critical angle $	heta_{c}$, where:

Accepted Answer

$\sin	heta_{c}=\frac{1}{1.5}$. At the critical angle the refracted ray grazes the surface ($	heta_{2}=90^{\circ}$): $\sin	heta_{c}=\frac{1}{n}=\frac{1}{1.5}$.

Question 6

When two waves meet, the resultant displacement is the sum of their individual displacements. This is the principle of:

Accepted Answer

Superposition. Superposition states displacements add. It underlies interference and standing waves.

Question 7

The bending and spreading of waves as they pass around obstacles or through gaps is called _____.

Accepted Answer

diffraction. Diffraction is most noticeable when the obstacle or gap is similar in size to the wavelength.

Question 8

The refractive index of a medium is $n=\frac{c}{v}$, where the speed of light is greatest in a _____.

Accepted Answer

vacuum. Light travels fastest in a vacuum, so $v1$.

Question 9

When a wavefront enters a slower medium at an angle, why does its direction change?

Accepted Answer

Different parts of the wavefront change speed at different times. Different parts of the wavefront reach the boundary at different times and slow down, so the wavefront changes direction (refraction).

Question 10

When a wave is refracted on entering a new medium, which quantity stays the same?

Accepted Answer

Its frequency. In refraction the frequency is unchanged; the speed and wavelength change.

IB Physics: Wave phenomena — Practice Questions & Answers

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