Edexcel A-Level Physics AS: Waves and Light

[Maximum number: 1]

The time period of a wave decreases.
Which of the following properties of the wave increases?

A

amplitude

B

frequency

C

speed

D

wavelength

[Maximum number: 8]

A student investigated the reflection of microwaves from a metal plate and a glass plate. The metal plate reflects microwaves and the glass plate partially reflects microwaves.

A plan view of the apparatus is shown.

The metal plate, the transmitter and the receiver were kept in fixed positions. The value of d was varied by moving the glass plate.

Figure for Question 2 — Edexcel A-Level Physics AS

(a)

As d varied, the intensity of the microwaves detected by the receiver varied.

Explain why.

[ 3 ]

(b)

The student recorded values of d when the receiver showed a maximum value of intensity.

He recorded d for a sequence of five maxima.

Maxima | 1 | 2 | 3 | 4 | 5
d / cm | 9.9 | 11.1 | 12.7 | 13.9 | 15.4

Figure for Question (b) — Edexcel A-Level Physics AS

[ 5 ]

(i)

Determine the wavelength of the microwaves being transmitted.

Wavelength =

[ 3 ]

(ii)

Calculate the frequency of the microwaves being transmitted.

Frequency =

Figure for Question (ii) — Edexcel A-Level Physics AS

[ 2 ]

[Maximum number: 12]

The photograph shows a musical instrument called a violin.

Figure for Question 3 — Edexcel A-Level Physics AS

The violin has four strings. Each string is held in a fixed position by a peg and at the bridge.

When a string is plucked, a stationary wave forms on the string.

(a)

Explain how a stationary wave forms on the string.
(3)

[ 3 ]

(b)

The simplest stationary wave has a node at each end and an antinode at the centre. Its frequency is the fundamental frequency.

String	Fundamental frequency / Hz
1	196
2	294
3	440
4	659

The tension is $71.5\,\mathrm{N}$ , length $0.32\,\mathrm{m}$ , and mass per unit length $2.03\times10^{-3}\,\mathrm{kg\,m^{-1}}$ . Deduce which string it is.

[ 4 ]

The wave speed is $v=\sqrt{\frac{T}{\mu}}=\sqrt{\frac{71.5}{2.03\times10^{-3}}}=187.7\,\mathrm{m\,s^{-1}}.$ For the fundamental, $\lambda=2L=0.64\,\mathrm{m}$ , so $f=v/\lambda=293\,\mathrm{Hz}$ , closest to string 2.

(c)

The stationary wave on the string causes sound waves to be transmitted through the air.

Describe the similarities and differences between the stationary wave on the string and the sound waves transmitted through the air.

[ 5 ]

[Maximum number: 2]

A student investigated the reflection of microwaves from a metal plate and a glass plate. The metal plate reflects microwaves and the glass plate partially reflects microwaves.

A plan view of the apparatus is shown.

The metal plate, the transmitter and the receiver were kept in fixed positions. The value of d was varied by moving the glass plate.

Figure for Question 4 — Edexcel A-Level Physics AS

The student recorded values of d when the receiver showed a maximum value of intensity.

He recorded d for a sequence of five maxima.

Maxima | 1 | 2 | 3 | 4 | 5
d / cm | 9.9 | 11.1 | 12.7 | 13.9 | 15.4

Calculate the frequency of the microwaves being transmitted.

Frequency =

[Maximum number: 5]

The photograph shows a musical instrument called a violin.

Figure for Question 5 — Edexcel A-Level Physics AS

The violin has four strings. Each string is held in a fixed position by a peg and at the bridge.

When a string is plucked, a stationary wave forms on the string.

The stationary wave on the string causes sound waves to be transmitted through the air.

Describe the similarities and differences between the stationary wave on the string and the sound waves transmitted through the air.

[Maximum number: 2]

Light is a transverse wave.

Describe the difference between transverse waves and longitudinal waves.

[Maximum number: 1]

A graph of displacement against time for a point on a transverse progressive wave is shown.

Figure for Question 7 — Edexcel A-Level Physics AS

Which of the following statements is correct?

A

The amplitude of the wave is 20 cm .

B

The frequency of the wave is 2.5 Hz .

C

The period of the wave is 0.2 s .

D

The wavelength of the wave is 0.4 m .

[Maximum number: 2]

A student investigated the interference of sound waves. The student used a signal generator with two loudspeakers, as shown.

Figure for Question 8 — Edexcel A-Level Physics AS

The student used this investigation to determine the speed of sound in air.

To determine an accurate value for the speed of sound, the student would need to use other apparatus.

Explain what other apparatus the student would need.

(As $v=f \lambda$ ) the frequency would need to be measured

- States suitable apparatus to measure frequency

Accept time period for frequency

Accept frequency meter, oscilloscope/CRO, sound sensor with datalogger, mobile phone with an app

[Maximum number: 3]

A student investigated the reflection of microwaves from a metal plate and a glass plate. The metal plate reflects microwaves and the glass plate partially reflects microwaves.

A plan view of the apparatus is shown.

The metal plate, the transmitter and the receiver were kept in fixed positions. The value of d was varied by moving the glass plate.

Figure for Question 9 — Edexcel A-Level Physics AS

As d varied, the intensity of the microwaves detected by the receiver varied.

Explain why.

[Maximum number: 3]

A student investigated the reflection of microwaves from a metal plate and a glass plate. The metal plate reflects microwaves and the glass plate partially reflects microwaves.

A plan view of the apparatus is shown.

The metal plate, the transmitter and the receiver were kept in fixed positions. The value of d was varied by moving the glass plate.

Figure for Question 10 — Edexcel A-Level Physics AS

The student recorded values of d when the receiver showed a maximum value of intensity.

He recorded d for a sequence of five maxima.

Maxima | 1 | 2 | 3 | 4 | 5
d / cm | 9.9 | 11.1 | 12.7 | 13.9 | 15.4

Determine the wavelength of the microwaves being transmitted.

Wavelength =

[Maximum number: 11]

A vibrating tuning fork is placed near to the open end of a tube that is closed at the other end, as shown.

Figure for Question 11 — Edexcel A-Level Physics AS

(a)

Describe how a stationary wave is formed inside the tube.

[ 6 ]

(b)

When the length of the tube was 20.4 cm , the simplest possible stationary wave was formed inside the tube.

[ 5 ]

(i)

Calculate the frequency of the sound produced by the tube. speed of sound in air $=340 \mathrm{~m} \mathrm{~s}^{-1}$

Frequency =

[ 3 ]

(ii)

The actual frequency of the sound produced by the tube is slightly less than the calculated value.

Suggest why.

[ 2 ]

[Maximum number: 3]

A student investigated how the frequency of vibration of a string varies with the tension in the string. The student connected masses to one end of the string and attached the other end to a vibrator as shown.

Figure for Question 12 — Edexcel A-Level Physics AS

A signal generator was connected to the vibrator. The signal generator was adjusted until a stationary wave was produced on the string. The stationary wave had nodes at both ends of the vibrating length of the string, L, and an antinode in the middle.

When W is $80.0 \mathrm{~N}, f$ is 659 Hz.

Calculate the mass per unit length of the string.
length $L=0.328 \mathrm{~m}$
(3)

Mass per unit length =

[Maximum number: 7]

A student investigated how the frequency of vibration of a string varies with the tension in the string. The student connected masses to one end of the string and attached the other end to a vibrator as shown.

Figure for Question 13 — Edexcel A-Level Physics AS

A signal generator was connected to the vibrator. The signal generator was adjusted until a stationary wave was produced on the string. The stationary wave had nodes at both ends of the vibrating length of the string, L, and an antinode in the middle.

(a)

The student changed the weight W applied to the string and adjusted the frequency f of the signal generator until the same stationary wave was set up on the string.

The student plotted a graph of $f^{2}$ against W.
Explain why the graph was a straight line through the origin.
(5)

[ 5 ]

(b)

Describe a method that can be used to confirm that the frequency value stated on the signal generator is correct.
(2)

[ 2 ]

[Maximum number: 3]

A red light-emitting diode (LED) was placed into a circuit, as shown.

Figure for Question 14 — Edexcel A-Level Physics AS

The LED emits light of wavelength of 627 nm and may be assumed to be 100% efficient. The battery has negligible internal resistance.

When the switch was closed, the reading on the ammeter was 9.2 mA.

The maximum intensity of sunlight at the Earth's surface is about $1100 \mathrm{Wm}^{-2}$ .

A student suggests that the intensity of light at a distance of 5.0 mm from an LED with a power of 0.69 W is greater than the intensity of sunlight at the Earth's surface.

Assess whether the student's suggestion is correct.

At $r=5.0\,\mathrm{mm}$ , $A=4\pi r^2=3.14\times10^{-4}\,\mathrm{m^2}$ . Therefore $I=P/A=0.69/(3.14\times10^{-4})=2.20\times10^3\,\mathrm{W\,m^{-2}}.$ This is greater than $1100\,\mathrm{W\,m^{-2}}$ , so the suggestion is correct.

[Maximum number: 4]

Light is a transverse wave.

(a)

Two prisms, A and B, made from different types of glass are placed in contact as shown. An incident ray of light enters prism A.

Figure for Question (a) — Edexcel A-Level Physics AS

air

[ 4 ]

(i)

State why the incident ray of light does not change direction as it enters prism A .

[ 1 ]

(ii)

Calculate the angle of refraction as this ray of light travels across the boundary between prism A and prism B.
refractive index of glass in prism A=1.40
refractive index of glass in prism B=1.55

Angle of refraction =

[ 3 ]

[Maximum number: 5]

A student determined the refractive index of a transparent material. The student had a semicircular block of the material as shown.

Figure for Question 16 — Edexcel A-Level Physics AS

(a)

Complete the diagram to show the critical angle.

[ 1 ]

(b)

Determine the refractive index of the transparent material, using measurements from the diagram.

Refractive index =

[ 2 ]

(c)

The student repeated the process for a second semicircular block of a different transparent material. Her measured critical angle was $C=41.0^\circ\pm0.5^\circ$ . Calculate the range of possible refractive-index values.

[ 2 ]

Use $n=1/\sin C$ at the limiting angles. For $C=40.5^\circ$ , n=1.54;
for $C=41.5^\circ$ , n=1.51. Thus the possible range is approximately 1.51 to 1.54.

(d)

The student had a rectangular block of transparent material and made the measurements shown. Deduce whether this block is made of the same material as the block in (b).

Figure for Question (d) — Edexcel A-Level Physics AS

[ 3 ]

(e)

The student used rays of white light.

Explain why using monochromatic light would increase the validity of the conclusion made in (c).

[ 3 ]

[Maximum number: 4]

The refractive index of glass varies with the colour of light.
refractive index of glass for red light =1.513
refractive index of glass for violet light =1.532

White light is incident on a boundary between glass and air, as shown.

Figure for Question 17 — Edexcel A-Level Physics AS

Explain what happens to the red light and the violet light when meeting the boundary. Your answer should include calculations.

[Maximum number: 2]

Light is a transverse wave.

The light emerging from prism B is observed through a polarising filter. The polarising filter is rotated gradually, and the light transmitted by the filter varies in intensity.

Explain how this observation demonstrates that light waves are transverse.

[Maximum number: 2]

Boats can shelter from waves on the sea in a harbour.

The diagram shows a harbour where boats can enter and leave through two gaps in the harbour wall.

Figure for Question 19 — Edexcel A-Level Physics AS

Waves on the sea are diffracted as they pass through the gaps in the harbour wall.

Describe how Huygens' construction can be used to predict the shape of diffracted wavefronts.

[Maximum number: 4]

A teacher has a laser pointer. The laser pointer emits a narrow beam of plane polarised light.

(a)

The teacher shines light from the laser pointer onto a diffraction grating as shown. This produces a diffraction pattern on a screen.

[ 4 ]

(i)

The diffraction grating equation is $n\lambda=d\sin\theta$ . State the quantity represented by d.

[ 1 ]

Distance between (adjacent) slits

Or grating spacing

Or line spacing

Or slit spacing

Or $\frac{1}{\text { lines per } m}$

(ii)

The distance from the central maximum to the first-order maximum is $1.61\,\mathrm{m}$ and the grating-to-screen distance is $2.74\,\mathrm{m}$ . The wavelength is $532\,\mathrm{nm}$ . Calculate the number of lines per millimetre on the diffraction grating.

[ 3 ]

$\tan\theta=1.61/2.74$ , so $\theta=30.4^\circ$ . Using $n\lambda=d\sin\theta$ gives $d=1.05\times10^{-6}\,\mathrm{m}$ . Therefore the grating has $1/d=9.52\times10^5\,\mathrm{m^{-1}}=952$ lines per millimetre (about 950).

[Maximum number: 2]

A beam of electrons passes through a thin layer of graphite. The electrons are then incident on a fluorescent screen, causing a series of rings to form, as shown.
beam of electrons

Figure for Question 21 — Edexcel A-Level Physics AS

Explain what the rings show about the nature of electrons.

[Maximum number: 5]

Niels Bohr developed an early model of the atom where electrons could only exist in fixed orbits around a nucleus. When an atom is ionised, an electron moves from its orbit around the nucleus to be free of the atom. Bohr derived an expression for the ionisation energy E, in joules, for a hydrogen atom:

$\left(\frac{e^2}{kh}\right)^2\times\frac{m}{8}$

where m is the mass of the electron, e is the charge of the electron, $k=8.85\times10^{-12}\,\mathrm{C\,V^{-1}m^{-1}}$ , and h is the Planck constant.

The Bohr model can also be used to predict an approximate radius for an atom. The equation for the radius r of the hydrogen atom is:

$r=\frac{h^2k}{\pi me^2}$

where m is the mass of the electron.

A student suggests that, for a speed of $1.4\times10^7\,\mathrm{m\,s^{-1}}$ , neutrons would have a wavelength similar to the radius of a hydrogen atom. Determine whether the student is correct.

mass of neutron $=1.67\times10^{-27}\,\mathrm{kg}$

Substitutes values into $r=\frac{h^{2} k}{\pi m e^{2}}$

(1)

$r=5.3 \times 10^{-11}(\mathrm{~m})$

(1)

Use of $\lambda=h / p$

(1)

$\lambda=2.8 \times 10^{-14}(\mathrm{~m})$ (for neutron)

(1)

neutron wavelength not similar to size of atom radius, so student is incorrect

(1)

(MP5 is dependent upon awarding all of MP1-4 and there needs to be some comparison of the two values)

(allow MP1 and/or MP3 for candidates who substitute the incorrect mass into the equation e.g. mass of neutron where it should be mass of electron in MP1)

$\mathrm{r}=5.31 \times 10^{-11} \mathrm{~m}$

For neutron, $\lambda=h / p=\left(6.63 \times 10^{-34} \mathrm{Js}\right) /\left(1.67 \times 10^{-27} \mathrm{~kg}\right)\left(1.4 \times 10^{7} \mathrm{~m} \mathrm{~s}^{-1}\right)$ $=2.84 \times 10^{-14} \mathrm{~m}$

[Maximum number: 4]

Light is a transverse wave.

Two prisms, A and B, made from different types of glass are placed in contact as shown. An incident ray of light enters prism A.

Figure for Question 23 — Edexcel A-Level Physics AS

air

The refractive index of the glass in prism B is greater than the refractive index of the glass in prism A. When the ray of light reaches the boundary between the prisms, some light is reflected and some is refracted.

Complete the diagram to show the two paths taken by the reflected and refracted light until they have returned to the air.

[Maximum number: 7]

Rolled steel joists (RSJs) are used in the construction of buildings, as shown.

Figure for Question 24 — Edexcel A-Level Physics AS

The strength of an RSJ is greatly reduced if there are air gaps within the steel. Ultrasound is used to detect any air gaps in the RSJ.

Pulses of ultrasound are sent by a transducer into an RSJ as shown. Any returning ultrasound is detected by the transducer.

(a)

Explain how this arrangement can be used to show whether the RSJ contains an air gap.

[ 4 ]

(b)

Ultrasound is a sound wave with a frequency greater than 20 kHz. The frequency of ultrasound used by the transducer in this method is 5 MHz.

Explain why a much higher frequency than 20 kHz is needed in this method.

[ 3 ]

[Maximum number: 6]

A red light-emitting diode (LED) was placed into a circuit, as shown.

Figure for Question 25 — Edexcel A-Level Physics AS

The LED emits light of wavelength of 627 nm and may be assumed to be 100% efficient. The battery has negligible internal resistance.

When the switch was closed, the reading on the ammeter was 9.2 mA.

(a)

Calculate the number of photons emitted by the LED in one minute.

Number of photons emitted in one minute =

[ 4 ]

In one minute the LED emits $E=Pt=0.11(60)=6.6\,\mathrm J$ . One photon has energy $hf=hc/\lambda=3.17\times10^{-19}\,\mathrm J$ . Therefore the number emitted is $6.6/(3.17\times10^{-19})=2.1\times10^{19}$ .

(b)

The red LED was replaced with a green LED which emits light with a shorter wavelength than the red LED. The current in the circuit did not change.

Explain how replacing the LED affected the number of photons emitted in one minute.

[ 2 ]

[Maximum number: 3]

The diagram shows the energy levels for an atom of hydrogen.

Figure for Question 26 — Edexcel A-Level Physics AS

Photons with energy $1.63\times10^{-18}\,\mathrm{J}$ are incident on a metal plate. The surface releases electrons due to the photoelectric effect.

Calculate the maximum possible speed of the electrons.

Work function $\Phi=5.89\times10^{-19}\,\mathrm{J}$ .

The maximum kinetic energy is $E_k=hf-\Phi=1.63\times10^{-18}-5.89\times10^{-19}=1.04\times10^{-18}\,\mathrm{J}.$ Using $E_k=\tfrac12m_ev_{\max}^2$ , $v_{\max}=\sqrt{\frac{2E_k}{m_e}}=1.5\times10^6\,\mathrm{m\,s^{-1}}.$

[Maximum number: 3]

Niels Bohr developed an early model of the atom where electrons could only exist in fixed orbits around a nucleus. When an atom is ionised, an electron moves from its orbit around the nucleus to be free of the atom. Bohr derived an expression for the ionisation energy E, in joules, for a hydrogen atom:

$\left(\frac{e^2}{kh}\right)^2\times\frac{m}{8}$

where m is the mass of the electron, e is the charge of the electron, $k=8.85\times10^{-12}\,\mathrm{C\,V^{-1}m^{-1}}$ , and h is the Planck constant.

Calculate E for a hydrogen atom, in eV.
(3)

E=\ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots . \mathrm{eV}

Substitute the constants into $E=\left(\frac{e^2}{kh}\right)^2\frac{m}{8}$ to obtain $E=2.17\times10^{-18}\,\mathrm{J}$ . Divide by $1.60\times10^{-19}\,\mathrm{J\,eV^{-1}}$ to give $13.56\,\mathrm{eV}$ (13.5 or 13.6 eV).

[Maximum number: 3]

The diagram shows the energy levels for an atom of hydrogen.

Figure for Question 28 — Edexcel A-Level Physics AS

Photons with energy $1.63\times10^{-18}\,\mathrm{J}$ are incident on a metal plate. The surface releases electrons due to the photoelectric effect.

Explain why the photoelectric effect demonstrates light behaving as a particle, rather than a wave.

[Maximum number: 6]

The diagram shows the energy levels for an atom of hydrogen.

Figure for Question 29 — Edexcel A-Level Physics AS

(a)

A photon has a wavelength of $218\,\mathrm{nm}$ .

[ 6 ]

(i)

Determine the energy, in $\mathrm{eV}$ , of this photon.

[ 4 ]

Using $c=f\lambda$ , $f=3.00\times10^8/(218\times10^{-9})=1.38\times10^{15}\,\mathrm{Hz}$ . Thus $E=hf=(6.63\times10^{-34})(1.38\times10^{15})=9.12\times10^{-19}\,\mathrm{J}=5.70\,\mathrm{eV}.$

(ii)

Explain whether the atom of hydrogen could emit a photon with this energy.
(2)

[ 2 ]

Edexcel A-Level Physics AS 2.3 Waves and Particle Nature of Light Questions

Exam points

Covered syllabus points

Covered syllabus points

Question 1

Question 2

Question (a)

Question (b)

Question (i)

Question (ii)

Question 3

Question (a)

Question (b)

Question (c)

Question 4

Question 5

Question 6

Question 7

Question 8

Question 9

Question 10

Question 11

Question (a)

Question (b)

Question (i)

Question (ii)

Question 12

Question 13

Question (a)

Question (b)

Question 14

Question 15

Question (a)

Question (i)

Question (ii)

Question 16

Question (a)

Question (b)

Question (c)

Question (d)

Question (e)

Question 17

Question 18

Question 19

Question 20

Question (a)

Question (i)

Question (ii)

Question 21

Question 22

Question 23

Question 24

Question (a)

Question (b)

Question 25

Question (a)

Question (b)

Question 26

Question 27

Question 28

Question 29

Question (a)

Question (i)

Question (ii)