Conduction — questions

1. identify

Each object below needs one thermal property. Match each object to the kind of material it should be made of.

Write the number of the matching option.

1. Thermal insulator
2. Good thermal conductor

• A baking tray: ______
• An oven glove: ______
• The panel of a room radiator: ______
• The walls of a picnic cool box: ______
• The base of an electric kettle: ______
• The lining of a winter boot: ______

Nudge (only if you are stuck): Ask what each object is for: passing energy on quickly, or keeping energy from getting through.

2. explain

On a hot summer afternoon, a steel slide and a plastic slide in a playground have been in the sun for hours. Both are at 45 °C. Which statement explains why the steel slide feels much hotter to touch?

Circle one answer.

• Plastic reflects more sunlight, so less energy reaches your hand.
• Steel stores more heat than plastic, so it feels hotter.
• Energy flows from your hand into the plastic, so it feels cool.
• Steel conducts well, so it passes energy into your skin faster.

Nudge (only if you are stuck): Your skin is at about 33 °C. Which way does energy flow when you touch a slide?

3. deduce

A pupil tests two rods of the same length and thickness, one brass and one stainless steel. One end of each stands in the same beaker of hot water, and a temperature sensor touches the far end of each rod. The table shows the readings. Which conclusion is correct?

Circle one answer.

• Brass is the better conductor: its far end warmed up faster.
• They conduct equally well: both rods started at 21 °C.
• Neither result counts: the far ends never reached the water temperature.
• Steel is the better conductor: it kept its energy in for longer.

Nudge (only if you are stuck): Energy enters each rod from the water. Which reading shows how fast it gets to the other end?

4. compare

The table shows when the pins dropped in a test of four rods of the same size, each pin 8 cm from a tank of hot water. Put the rods in order, best thermal conductor first.

Write the number of each step in order.

1. Iron
2. Glass
3. Aluminium
4. Brass

• First: ______
• Second: ______
• Third: ______
• Last: ______

Nudge (only if you are stuck): A pin drops when enough energy has been conducted along the rod to melt its wax.

5. describe / state / predict

Describe an experiment to show that aluminium is a better thermal conductor than plastic. You have an aluminium block, a plastic block and two ice cubes, and no hot water. (a) State how you set up the apparatus. (b) State three things you keep the same. (c) State what you measure. (d) Predict the result, and state what it shows.

(a) Apparatus

(b) Kept the same

(c) Measured

(d) Predicted result

Nudge (only if you are stuck): Think of something you can time that shows how fast energy reaches each ice cube.

6. explain

In a test of an aluminium rod and a steel rod, the pin on the aluminium rod is stuck on 6 cm from the hot water, and the pin on the steel rod 12 cm away. The aluminium pin drops first. Which statement explains why this does not show that aluminium is the better conductor?

Circle one answer.

• Aluminium is a worse conductor than steel, so the result must be wrong.
• Steel needs longer to warm up, so the test did not run for long enough.
• The aluminium pin was nearer the water, so it could drop first for that reason.
• The test should have used thicker rods, so that the pins would drop faster.

Nudge (only if you are stuck): What else, apart from the material, was different between the two rods?

7. identify / calculate

A pupil repeats the same fair test on one brass rod four times, timing how long its pin takes to drop. The table shows the results. (a) Identify the anomalous result: give its run number. (b) Calculate the mean time, leaving out the anomalous result. Give your answer to 3 significant figures.

(a) Run number of the anomalous result: ______________ unit ________

(b) Mean time: ______________ unit ________

Nudge (only if you are stuck): An anomalous result is one that does not fit the pattern of the others.

8. explain

A rod of stone is heated at one end. How is thermal energy passed along it?

Circle one answer.

• The particles at the hot end grow bigger and push the energy along.
• Free electrons pick up energy at the hot end and carry it along the rod.
• Hot particles of stone travel along the rod and take the energy with them.
• Particles at the hot end vibrate more and pass the vibration to their neighbours.

Nudge (only if you are stuck): Which particles could carry energy through this material, and what can they do in a solid?

9. identify

A copper wire and a rubber tube are each heated at one end. Which row shows correctly the ways in which thermal energy is conducted along each of them?

Circle one answer.

• A
• B
• C
• D

Nudge (only if you are stuck): Ask about each material on its own: is it a solid, and is it a metal?

10. state / explain

A steel skewer and a wooden skewer of the same size are pushed into a hot baked potato. (a) State the way of passing energy along that happens in both skewers. (b) Explain, in terms of particles, why the end of the steel skewer gets hot so much sooner.

(a) In both skewers

(b) Why the steel is faster

Nudge (only if you are stuck): For (b), ask what steel has that wood does not.

11. explain

A bottle of milk is wrapped in bubble wrap to keep it cold on a picnic. Which statement explains why the air in the bubbles is a bad thermal conductor?

Circle one answer.

• Its particles are light, so each one is too small to carry energy.
• Its particles are far apart, so they rarely collide to pass on energy.
• The air in the bubbles is cold, so it passes cold into the milk.
• Its particles are far apart, so they cannot vibrate or move at all.

Nudge (only if you are stuck): How far apart are the particles of a gas, and how does one particle pass energy to another?

12. explain / predict

A deep glass tank of water at 19 °C has a temperature sensor lying on the bottom. An electric heater is held just under the water surface, and the water is not stirred. After 20 minutes the water at the top is at 70 °C, but the sensor still reads 19 °C. (a) Explain, in terms of particles, why so little energy reaches the sensor. (b) The test is repeated with cooking oil instead of water. Predict whether the sensor reading now rises quickly, and give a reason. (c) A liquid metal such as mercury is too poisonous to use in school. Predict how the result would differ with it, and explain why in terms of particles.

(a) Why so little energy arrives

(b) Cooking oil

(c) Mercury

Nudge (only if you are stuck): Compare the particles of a liquid with those of a solid. For (b) and (c), which particles could carry energy quickly through each liquid?

13. identify

The table gives the thermal conductivity of six materials. A bigger number means that the material conducts thermal energy better. Match each material to its group.

Write the number of the matching option.

1. Thermal insulator
2. Good thermal conductor
3. In between

• Granite: ______
• Cork: ______
• Brass: ______
• Porcelain: ______
• Rubber: ______
• Steel: ______

Nudge (only if you are stuck): List the numbers in order and look for the big jumps between them.

14. explain / suggest

A clothes iron has a heavy aluminium plate on the bottom, heated by an element inside, and a hollow plastic handle with air inside. (a) Explain why the plate is made of aluminium. (b) Explain why the handle is made of plastic. (c) Supplement. Explain, in terms of particles, how a small amount of energy still reaches the top of the plastic handle. (d) Supplement. Suggest why a hollow handle with air inside stays cooler than a solid plastic handle.

(a) Aluminium plate

(b) Plastic handle

(c) Supplement: energy through the plastic

(d) Supplement: the hollow handle

Nudge (only if you are stuck): Which part should let energy through quickly, and which slowly? For (d), compare a gas with a solid.