Chapter 3 Quizzes | Topic 3 Waves

Quiz 1 — Types and definitions

1. In a transverse wave the oscillations are A. parallel to the energy transfer B. in random directions C. perpendicular to the energy transfer D. only along the normal

Specification 3.2. Light and water ripples are transverse.

2. Sound waves in air are A. longitudinal and can be reflected B. transverse electromagnetic waves C. unable to refract D. a flow of air molecules from source to ear

3.23 and 3.4: energy travels; matter does not travel with the wave.

3. Amplitude is A. the distance from one peak to the next B. the maximum displacement from the rest position C. the number of waves per second D. the time for one wave

Peak-to-peak is twice the amplitude if the wave is symmetric.

4. Wavelength can be measured as A. rest position to a peak B. the height of a peak C. the time between two peaks D. the distance between two neighbouring compressions

Or peak to next peak — two points in phase.

5. A wavefront is A. a line joining points that are in phase B. the amplitude of the wave C. the speed of the wave D. a particle that travels with the wave

On a ripple tank, a wavefront is a line along a crest.

Quiz 2 — $v=f\lambda$ and $T=1/f$

1. $f=5.0\,\text{Hz}$, $\lambda=0.40\,\text{m}$. The speed is A. $0.080\,\text{m/s}$ B. $2.0\,\text{m/s}$ C. $12.5\,\text{m/s}$ D. $5.4\,\text{m/s}$

$v=f\lambda=2.0\,\text{m/s}$.

2. Ripples: $f=2.5\,\text{Hz}$, $\lambda=8.0\,\text{cm}$. Speed is A. $20\,\text{m/s}$ B. $0.32\,\text{m/s}$ C. $0.20\,\text{m/s}$ D. $3.2\,\text{m/s}$

$\lambda=0.080\,\text{m}$, $v=0.20\,\text{m/s}$. A forgot to convert cm.

3. Period $T=0.020\,\text{s}$. Frequency is A. $50\,\text{Hz}$ B. $0.020\,\text{Hz}$ C. $20\,\text{Hz}$ D. $2.0\,\text{Hz}$

$f=1/T=50\,\text{Hz}$.

4. A radio wave of $100\,\text{MHz}$ in air ($3.0\times 10^8\,\text{m/s}$) has wavelength A. $3.0\times 10^{16}\,\text{m}$ B. $0.33\,\text{m}$ C. $3.0\times 10^6\,\text{m}$ D. $3.0\,\text{m}$

$f=1.00\times 10^8\,\text{Hz}$, $\lambda=v/f=3.0\,\text{m}$.

5. If frequency doubles and speed stays the same, wavelength A. doubles B. halves C. stays the same D. becomes zero

$\lambda=v/f$. Same $v$, larger $f$, smaller $\lambda$.

Quiz 3 — Doppler, reflection and refraction

1. A siren moves towards you. Compared with the source frequency, you hear A. a higher frequency and a shorter wavelength B. a lower frequency and a longer wavelength C. the same frequency and a shorter wavelength D. a higher frequency and a longer wavelength

Wavefronts bunch up in front of the source.

2. In the Doppler effect the frequency produced by the source A. always increases B. always decreases C. does not change D. becomes zero when the source moves

Only the observed frequency and wavelength change.

3. This change of observed frequency when a source moves is called A. refraction B. the Doppler effect C. total internal reflection D. diffraction

Specification 3.8.

4. Which statement is correct? A. Only light can be refracted B. Sound cannot be reflected C. Water waves cannot be refracted D. All waves can be reflected and refracted

Specification 3.9. An echo is reflected sound.

5. An echo is evidence that A. sound waves can be reflected B. sound is a transverse wave C. air molecules travel to the wall and back D. sound cannot travel in air

Energy reflects; the air does not travel to the cliff.

Quiz 4 — Electromagnetic spectrum

1. In order of increasing frequency the spectrum is A. gamma, X-ray, UV, visible, IR, micro, radio B. radio, IR, micro, visible, UV, X-ray, gamma C. radio, micro, IR, visible, UV, X-ray, gamma D. visible, radio, micro, IR, UV, X-ray, gamma

Radio longest $\lambda$, lowest $f$.

2. In a vacuum all EM waves travel at A. $3.0 \times 10^8\,\text{m/s}$ B. $340\,\text{m/s}$ C. different speeds depending on frequency D. $3.0 \times 10^8\,\text{km/h}$

Same speed in free space (3.10). $340\,\text{m/s}$ is sound in air.

3. A specification use of microwaves is A. sterilising medical equipment B. satellite transmissions C. fluorescent lamps D. medical X-ray images

3.12: cooking and satellite transmissions.

4. Excessive ultraviolet exposure can cause A. internal heating of body tissue only B. skin burns from infrared only C. no damage if you cannot see it D. damage to surface cells and blindness

Specification 3.13. Protect with sunscreen, clothing, UV filters.

5. Gamma rays are used to A. sterilise food and medical equipment B. cook food in a microwave oven C. broadcast FM radio D. take ordinary holiday photographs

3.12. Hazard: cancer / mutation.

Quiz 5 — Reflection, Snell’s law and TIR

1. The law of reflection states that A. $i + r = 90^\circ$ B. $i = r$, both measured from the normal C. $i = r$, both measured from the mirror surface D. $n = \sin i / \sin r$

C is the classic wrong measurement.

2. $i=40^\circ$, $r=25^\circ$. Refractive index is about A. $1.52$ B. $0.66$ C. $15$ D. $65$

$\sin 40/\sin 25=1.52$. B inverted the fraction.

3. Light going from air into glass at an angle A. speeds up and bends away from the normal B. slows down and does not change direction C. slows down and bends towards the normal D. is always totally internally reflected

TIR cannot start from air into glass.

4. Total internal reflection requires A. air to glass and $i < c$ B. glass to air and $i = 0$ C. any boundary as long as $i=r$ D. denser to rarer and $i > c$

Both conditions. Optical fibres use this.

5. For $n=1.50$ the critical angle is found from A. $\sin c = 1/1.50$, so $c \approx 41.8^\circ$ B. $c = 1.50^\circ$ C. $c = 90^\circ / 1.50$ D. $\sin c = 1.50$

$\sin c = 1/n$, then $\sin^{-1}$. $\sin c$ cannot be $1.50$.