MYP 4 & 5 · Physics
P2 - Heat, light and sound
25 questions across 11 sub-topics
Use the Sub-Topic filter above to focus on one.
P2.2 - Density
P2.3 - Changes of state, latent heat, heating and cooling curves
P2.5 - Temperature scales, conversions, absolute zero and internal energy
P2.7 - Pressure-temperature relationships and thermal processes
P2.8 - Heat capacity and specific heat capacity
P2.10 - Conduction, convection, radiation and insulation
P2.11 - Reflection and image formation in plane and curved mirrors
P2.13 - Refractive index and Snell's law
P2.14 - Critical angle, total internal reflection, prisms and optical fibres
P2.17 - Sound production, frequency, pitch and intensity
P2.18 - Oscilloscope traces and measuring the speed of sound
P2.2 - Density 2 questions
QUESTION 1
1 mark
Criterion A
Easy
Density of objects made from one metal
A set of toy soldiers has different sizes but all are made from the same metal.
Compare their densities and masses.
Show complete worked solution
The material fixes the density, so all have the same density. Their different volumes mean their masses may differ.
QUESTION 2
7 marks
Criterion B
Hard
Density of an irregular pendant
A student has a Eureka can, measuring cylinder and mass balance.
a.
State the two quantities that must be measured.
[2] b.
Describe a method to determine its density.
[5] Show complete worked solution
(a)
Measure the mass and volume of the pendant.
(b)
Measure the mass \(m\) using the balance. Fill the Eureka can until water is level with the spout and allow excess to drain. Submerge the pendant fully and collect the displaced water in the measuring cylinder. Its volume equals the pendant volume \(V\). Repeat if needed, then calculate \[\rho=\frac{m}{V}\]using consistent units.
P2.3 - Changes of state, latent heat, heating and cooling curves 2 questions
QUESTION 1
12 marks
Criterion A
Hard
Changes of state and particle model
Use the particle model to explain solids and changes between liquid and gas.
a(i).
Describe particle arrangement and movement in a solid.
[2] a(ii).
Name the state with the greatest average energy per particle.
[1] b(i).
Name the change from solid to liquid.
[1] b(ii).
Explain why temperature stays constant while melting.
[2] c(i).
Name the other process by which a liquid becomes a gas and distinguish it from boiling.
[3] c(ii).
Explain evaporative cooling.
[3] Show complete worked solution
(a(i))
Particles are closely packed in a fixed, regular arrangement and vibrate about fixed positions.
(a(ii))
Gas.
(b(i))
Melting.
(b(ii))
The supplied energy is used to overcome attractive forces between particles and increase potential energy, rather than increase average kinetic energy, so temperature remains constant.
(c(i))
Evaporation. It occurs at the surface and can happen below the boiling point, whereas boiling occurs throughout the liquid at a fixed temperature.
(c(ii))
The fastest surface particles escape. The remaining particles have lower average kinetic energy, so the liquid’s temperature falls.
QUESTION 2
3 marks
Criterion C
Medium
Interpreting a heating curve
The graph shows temperature as a substance is heated.
a.
Describe what happens from 3 to 8 minutes.
[1] b.
State its melting and boiling points.
[2] Show complete worked solution
(a)
The substance is melting while its temperature remains constant.
(b)
From the two plateaus, \[T_m=-7\ ^\circ\mathrm{C},\qquad T_b=58\ ^\circ\mathrm{C}\]
P2.5 - Temperature scales, conversions, absolute zero and internal energy 2 questions
QUESTION 1
6 marks
Criterion A
Medium
Kelvin and Celsius temperature scales
A gas is cooled. Complete the temperature reasoning and conversion table.
| Temperature / K | Temperature / °C |
|---|---|
| 10 | ? |
| ? | 631 |
a(i).
State the effect on average particle speed.
[1] a(ii).
Explain why a minimum possible temperature exists.
[2] a(iii.
State absolute zero in degrees Celsius.
[1] b.
Complete the two conversions.
[2] Show complete worked solution
(a(i))
The average speed decreases.
(a(ii))
Cooling reduces the particles’ average kinetic energy. Kinetic energy cannot be less than its minimum value, so temperature also has a lower limit.
(a(iii)
\[-273\ ^\circ\mathrm{C}\]
(b)
\[10\ \mathrm{K}=10-273=-263\ ^\circ\mathrm{C}\]\[631\ ^\circ\mathrm{C}=631+273=904\ \mathrm{K}\]
QUESTION 2
14 marks
Criterion C
Hard
Heating curves and gas volume
A solid is heated with constant electrical power.
| Time / s | Temperature / °C |
|---|---|
| 0 | 20.0 |
| 100 | 27.5 |
| 200 | 36.0 |
| 300 | 45.0 |
| 400 | 53.5 |
| 500 | 57.0 |
| 600 | 57.0 |
a(i).
Name one control variable.
[1] a(ii).
Explain why it is controlled.
[1] b(i).
Plot the results.
[3] b(ii).
Draw a curve of best fit.
[2] c(i).
Identify the state after the boiling plateau.
[1] c(ii).
Identify the point representing boiling.
[1] c(iii.
Explain why temperature remains constant during the plateau.
[2] d(i).
Describe volume-temperature behaviour at constant pressure.
[1] d(ii).
Estimate volume at 25 °C from a graph calibrated to 6.1 cm³ at 298 K.
[2] Show complete worked solution
(a(i))
Heater power, mass of material, starting temperature or room conditions.
(a(ii))
So changes in temperature can be attributed to heating time rather than another variable.
(b(i))
Use sensible labelled scales and plot all seven points accurately.
(b(ii))
Draw a smooth rising curve that levels at 57 °C after about 500 s.
(c(i))
Gas.
(c(ii))
The flat high-temperature section where the state changes from liquid to gas.
(c(iii)
Transferred energy breaks intermolecular attractions and increases potential energy rather than average kinetic energy, so temperature stays constant.
(d(i))
Volume increases approximately in direct proportion to absolute temperature.
(d(ii))
\[T=25+273=298\ \mathrm{K}\]\[V\approx\boxed{6.1\ \mathrm{cm^3}}\]
P2.7 - Pressure-temperature relationships and thermal processes 2 questions
QUESTION 1
3 marks
Criterion A
Hard
Gas pressure at constant volume
A sealed rigid container holds gas at 288 K and 107 kPa. It is heated to 405 K.
Calculate the new pressure.
Show complete worked solution
At constant volume, \(p/T\) is constant: \[\frac{p_1}{T_1}=\frac{p_2}{T_2}\]\[p_2=107\left(\frac{405}{288}\right)=150.5\ \mathrm{kPa}\approx\boxed{150\ \mathrm{kPa}}\]
QUESTION 2
9 marks
Criterion A
Hard
Compressing and heating a gas
A piston traps 0.014 m³ of gas at 98 kPa.
a(i).
State and explain the pressure change when the volume is reduced.
[3] a(ii).
At constant temperature the volume becomes 0.013 m³. Calculate the new pressure.
[3] b.
The fixed-volume gas is heated. Explain the pressure change.
[3] Show complete worked solution
(a(i))
Pressure increases. In the smaller volume, particles strike each unit area of wall more frequently, increasing the average force per unit area.
(a(ii))
\[p_1V_1=p_2V_2\]\[p_2=\frac{(98)(0.014)}{0.013}=105.5\ \mathrm{kPa}\approx\boxed{110\ \mathrm{kPa}}\]
(b)
Particles gain average kinetic energy and move faster. They collide with the walls more frequently and with greater momentum change, so force per unit area and pressure increase.
P2.8 - Heat capacity and specific heat capacity 3 questions
QUESTION 1
1 mark
Criterion A
Easy
Definition of specific heat capacity
Specific heat capacity is a property of a material.
State its definition.
Show complete worked solution
The specific heat capacity is the energy needed to raise the temperature of 1 kg of a substance by 1 °C (or 1 K).
QUESTION 2
11 marks
Criterion B
Hard
Specific heat capacity of liquids
Identical coils transfer 126 kJ to 1.0 kg of water and 1.0 kg of oil. Both start at 18 °C; oil reaches 93 °C.
a.
Define specific heat capacity.
[1] b.
Explain the effect of an insulating lid on accuracy.
[2] c.
Explain why equal masses are used.
[2] d.
Calculate the specific heat capacity of the oil.
[4] e.
Explain why water is usually preferred in heating systems.
[2] Show complete worked solution
(a)
Energy required to raise the temperature of \(1\ \mathrm{kg}\) of a substance by \(1^\circ\mathrm{C}\).
(b)
It reduces energy transfer to surroundings, so a greater fraction of heater energy warms the liquid and the calculated value is closer to the true value.
(c)
Temperature change depends on mass as well as specific heat capacity. Keeping mass equal makes the liquid type the main cause of any difference.
(d)
\[\Delta T=93-18=75^\circ\mathrm{C}\]\[c=\frac{Q}{m\Delta T}=\frac{126000}{(1.0)(75)}=\boxed{1680\ \mathrm{J\,kg^{-1}\,K^{-1}}}\]
(e)
Water has higher specific heat capacity, so each kilogram transports more energy for the same temperature decrease.
QUESTION 3
8 marks
Criterion B
Hard
Measuring specific heat capacity
A student has an insulated flask, mass balance, joulemeter, thermometer, power supply and immersion heater.
| Liquid | Mass / kg | Temperature change / °C | c / J kg⁻¹ °C⁻¹ |
|---|---|---|---|
| A | 0.30 | 12 | 4200 |
| B | 0.30 | 23 | 2200 |
| C | 0.30 | 25 | ? |
a.
Describe a method to determine specific heat capacity.
[5] b.
Each sample receives 15 kJ. Calculate c for liquid C.
[3] Show complete worked solution
(a)
Find the liquid mass by difference using the balance. Place the heater and thermometer in the insulated liquid. Record the initial temperature, switch on the heater and measure the transferred energy \(Q\) with the joulemeter. Record the temperature rise \(\Delta T\), repeat, and calculate \[c=\frac{Q}{m\Delta T}\]
(b)
\[Q=15000\ \mathrm{J}\]\[c=\frac{15000}{(0.30)(25)}=\boxed{2000\ \mathrm{J\,kg^{-1}\,^{\circ}C^{-1}}}\]
P2.10 - Conduction, convection, radiation and insulation 6 questions
QUESTION 1
4 marks
Criterion A
Medium
Direction and rate of heating
Three flasks contain equal volumes of water. They are surrounded by gel initially at 50 °C. The flask temperatures are shown.
a.
For each flask, name the main heating mechanism between water and gel and state the direction of net transfer.
[2] b.
Identify which flask transfers energy to the gel fastest and explain.
[2] Show complete worked solution
(a)
Energy crosses the glass mainly by conduction and between exposed surfaces by infrared radiation. Net energy moves from the hotter material to the cooler material.
(b)
Flask C is hottest, so it has the largest temperature difference from the 50 °C gel. A larger temperature difference gives a greater rate of thermal transfer.
QUESTION 2
6 marks
Criterion B
Hard
Cooling and insulation investigation
A student varies the thickness of a cotton-wool jacket around a beaker and records water temperature after 3 min.
a.
State the independent variable.
[1] b.
Give one control variable.
[1] c.
Explain how trapped air reduces convection.
[2] d(i).
Describe how to process three repeats.
[1] d(ii).
State the conclusion shown by the trend.
[1] Show complete worked solution
(a)
Thickness of the cotton-wool jacket.
(b)
Initial water temperature, water volume, beaker type or cooling time.
(c)
Air pockets cannot circulate. This suppresses convection currents and reduces energy transfer from the beaker.
(d(i))
Identify anomalies and calculate a mean final temperature for each thickness.
(d(ii))
Increasing insulation thickness leaves the water at a higher final temperature, so cooling rate decreases.
QUESTION 3
3 marks
Criterion A
Medium
Conduction through a solid
One end of a solid block is heated.
Name the main transfer mechanism and explain it using particles.
Show complete worked solution
The mechanism is conduction. Particles near the hot end gain kinetic energy and vibrate more. Collisions and interactions transfer energy to neighbouring particles, so energy passes through the solid.
QUESTION 4
7 marks
Criterion B
Hard
Convection in a water loop
A rectangular glass tube is filled with cold water and heated at one lower corner.
a.
State one state of matter in which convection cannot occur and explain.
[2] b(i).
Draw two arrows showing the circulation of the water.
[1] b(ii).
Explain the circulation.
[3] c.
Which is not convection: room heating by radiator, water heating in a kettle, heating through a copper pan, or hot air rising in a chimney?
[1] Show complete worked solution
(a)
Convection cannot occur in a solid because its particles are not free to move through the material.
(b(i))
Draw water rising above the heater, moving across the top, descending on the other side, and returning along the bottom.
(b(ii))
Water near the heater gains internal energy, expands and becomes less dense, so it rises. Cooler, denser water sinks and moves in to replace it, producing a convection current.
(c)
Heating through the solid copper pan is conduction, so that is the non-convection example.
QUESTION 5
3 marks
Criterion B
Medium
Leslie cube investigation
A Leslie cube has matt black, shiny black, matt white and shiny white faces and is filled with hot water.
a.
Predict the face that gives the greatest infrared reading.
[1] b.
Predict the face that gives the smallest reading.
[1] c.
Suggest one improvement to a hand-based comparison.
[1] Show complete worked solution
(a)
The matt black face is the best infrared emitter and gives the greatest reading.
(b)
The shiny white face is the poorest emitter and gives the smallest reading.
(c)
Use an infrared detector at the same measured distance from each face and repeat each reading.
QUESTION 6
3 marks
Criterion A
Medium
Insulated takeaway cup
A paper cup is wrapped in corrugated cardboard that traps small pockets of air.
Explain how the design reduces the cooling rate.
Show complete worked solution
Paper, cardboard and trapped air have low thermal conductivity, so conduction is slow. The trapped air cannot circulate freely, so convection currents are reduced. Therefore less energy leaves the drink each second.
P2.11 - Reflection and image formation in plane and curved mirrors 1 question
QUESTION 1
7 marks
Criterion A
Hard
Reflection and refraction
A student directs a light ray at a plane mirror and then at a glass block.
a(i).
State the law of reflection.
[1] a(ii).
Define diffuse reflection.
[1] b.
Draw a ray diagram for an angle of incidence of 35°.
[2] c.
Explain why the ray changes direction on entering glass and name the effect.
[3] Show complete worked solution
(a(i))
\[\text{angle of incidence}=\text{angle of reflection}\]Both angles are measured from the normal.
(a(ii))
Diffuse reflection occurs when an uneven surface reflects incident rays in many different directions.
(b)
Draw the incident ray making 35° with the normal and an arrow towards the mirror. Draw the reflected ray on the other side of the normal, also at 35°, with an arrow away from the mirror.
(c)
Light travels at a different speed in glass than in air. At an oblique boundary, one side of the wavefront changes speed first, so the ray changes direction. This is refraction.
P2.13 - Refractive index and Snell's law 2 questions
QUESTION 1
8 marks
Criterion C
Hard
Finding refractive index from a graph
A student measures refraction angles for a transparent block.
| i | 10.0° | 20.0° | 30.0° | 40.0° | 50.0° | 60.0° |
|---|---|---|---|---|---|---|
| r | 8.3° | 16.4° | 24.8° | 32.3° | 39.8° | 46.2° |
| sin i | 0.174 | 0.342 | 0.500 | 0.643 | 0.766 | 0.866 |
| sin r | 0.144 | 0.282 | 0.419 | 0.534 | 0.640 | 0.722 |
a.
Plot sin r against sin i and draw a straight best-fit line through the origin.
[4] b(i).
Calculate the gradient of the graph.
[2] b(ii).
The gradient equals 1/n. Calculate the refractive index.
[2] Show complete worked solution
(a)
Plot all six points using more than half of each axis. Label both axes, use a sensible scale and draw a straight best-fit line through the origin.
(b(i))
Using representative points on the best-fit line,\[m=\frac{\Delta(\sin r)}{\Delta(\sin i)}\approx\frac{0.50}{0.60}=0.833\]
(b(ii))
\[n=\frac{1}{m}=\frac{1}{0.833}=1.20\]Refractive index has no unit.
QUESTION 2
9 marks
Criterion A
Hard
Dispersion at an air-glass boundary
White light enters glass at 45.0°. The refractive indices are 1.514 for red light and 1.528 for violet light.
a.
Calculate the angle of refraction for red light.
[3] b.
Explain why light does not separate into colours when it enters along the normal.
[2] c.
Calculate the angular separation between the red and violet rays.
[4] Show complete worked solution
(a)
\[n=\frac{\sin i}{\sin r}\]\[\sin r=\frac{\sin45.0^\circ}{1.514}=0.46705\]\[r=\sin^{-1}(0.46705)=27.8^\circ\]
(b)
Dispersion requires the colours to refract by different angles. Along the normal, the angle of incidence is 0°, so none of the colours changes direction.
(c)
\[r_v=\sin^{-1}\!\left(\frac{\sin45.0^\circ}{1.528}\right)=27.566^\circ\]\[\theta=27.843^\circ-27.566^\circ=0.277^\circ\]
P2.14 - Critical angle, total internal reflection, prisms and optical fibres 3 questions
QUESTION 1
5 marks
Criterion A
Hard
Critical angle in an optical fibre
An optical-fibre core has refractive index 1.54.
a.
Calculate the critical angle at a core-air boundary.
[3] b.
Explain why bending the fibre too sharply can reduce image quality.
[2] Show complete worked solution
(a)
\[\sin C=\frac{1}{n}=\frac{1}{1.54}\]\[C=\sin^{-1}(0.64935)=40.5^\circ\]
(b)
A sharp bend can make some rays meet the core-cladding boundary at an angle no greater than the critical angle. Those rays refract out instead of undergoing total internal reflection, so less light reaches the detector.
QUESTION 2
12 marks
Criterion B
Hard
Optical fibres and critical angle
An optical fibre core has refractive index 1.5.
a.
Explain why light remains inside an optical fibre.
[2] b(i).
Describe an experiment to measure refractive index of a rectangular block.
[4] b(ii).
State one laser hazard and precaution.
[2] c.
Calculate the critical angle.
[4] Show complete worked solution
(a)
At the core boundary the incidence angle exceeds the critical angle, so light undergoes total internal reflection repeatedly.
(b(i))
Trace the block, direct a narrow ray into it and mark incident and emergent rays. Remove the block, join the internal path, draw a normal, then measure \(i\) and \(r\). Calculate \(n=\sin i/\sin r\); repeat and average.
(b(ii))
A laser beam may damage the retina. Keep it below eye level, never look into it, and use appropriate eye protection.
(c)
\[\sin c=\frac{1}{n}=\frac{1}{1.5}\]\[c=\sin^{-1}(0.6667)=\boxed{42^\circ}\]
QUESTION 3
5 marks
Criterion A
Hard
Acrylic boundaries
A semicircular acrylic block is in water. The acrylic-water critical angle is 63.2°. A second ray meets an acrylic-air boundary as shown.
a.
Define the critical angle.
[1] b.
Describe what happens at the acrylic-water boundary for incidence 75°.
[1] c.
The acrylic-air critical angle is 41.8°. Calculate the refractive index of acrylic.
[3] Show complete worked solution
(a)
The critical angle is the angle of incidence in the optically denser medium for which the angle of refraction is 90°.
(b)
Since 75° exceeds 63.2°, the ray undergoes total internal reflection back into the acrylic.
(c)
\[n=\frac{1}{\sin C}=\frac{1}{\sin41.8^\circ}=1.50\]
P2.17 - Sound production, frequency, pitch and intensity 1 question
QUESTION 1
9 marks
Criterion B
Hard
Measuring the speed and frequency of sound
A signal generator, speaker, two microphones and oscilloscope are used to investigate sound.
| Statement |
|---|
| Measure the distance between the microphones; this is one wavelength. |
| Stop moving microphone 2 when the traces line up again. |
| Use the measured distance and generator frequency to calculate wave speed. |
| Begin with both microphones at equal distance from the speaker. |
| Keep microphone 1 fixed and move microphone 2 away until the phase changes. |
a(i).
Put the five method statements in the correct order.
[3] a(ii).
For frequency 50 Hz and microphone separation 6.8 m, calculate sound speed.
[2] b(i).
State the quantity X marked across one complete trace cycle.
[1] b(ii).
One division is 0.005 s and one cycle spans 8 divisions. Calculate frequency.
[2] b(iii.
Sketch a louder sound with the same frequency.
[1] Show complete worked solution
(a(i))
1 Begin with both microphones equally distant from the speaker. 2 Keep microphone 1 fixed and move microphone 2 away. 3 Stop when the traces line up again. 4 Measure the microphone separation; this is one wavelength. 5 Use the wavelength and generator frequency to calculate wave speed.
(a(ii))
\[v=f\lambda=(50)(6.8)=340\ \mathrm{m\,s^{-1}}\]
(b(i))
X is the time period, option D.
(b(ii))
\[T=8(0.005)=0.040\ \mathrm{s}\]\[f=\frac{1}{T}=\frac{1}{0.040}=25\ \mathrm{Hz}\]
(b(iii)
Draw a wave with the same horizontal period but a larger vertical amplitude.
P2.18 - Oscilloscope traces and measuring the speed of sound 1 question
QUESTION 1
6 marks
Criterion A
Hard
Echoes, pitch and oscilloscope traces
A student hears an echo in an empty drama hall but not on an open playing field. Two students’ voices are later displayed on an oscilloscope.
a.
Explain why an echo is heard in the hall.
[1] b.
Suggest one other change as sound crosses a wall, besides speed and wavelength.
[1] c(i).
State the normal human audible frequency range.
[1] c(ii).
A male student’s voice has lower pitch. Compare its frequency with the female student’s voice.
[2] d.
Does trace A represent the male or female voice? Justify.
[1] Show complete worked solution
(a)
Sound reflects from the hall walls and returns after the direct sound. The open field has no nearby large reflecting surfaces.
(b)
The ray may refract and change direction; its amplitude may also decrease as energy is absorbed.
(c(i))
Approximately \(20\ \mathrm{Hz}\) to \(20\,000\ \mathrm{Hz}\).
(c(ii))
The male voice has lower frequency because pitch increases with frequency.
(d)
Trace A represents the female voice because it completes more cycles in the same time, so it has the higher frequency and pitch.