P2: Energy Transfers by Heating

Question 1

How can you find out what material is the best conductor?

Answer 1

Use different materials of rod with the same size. Each rod is coated with wax at one end. The uncoated ends are heated and the best conductors are the ones where the wax melts the quickest.

Question 2

What is thermal conductivity?

Answer 2

The greater the thermal conductivity of a material, the more energy per second it transfers by conduction through the material.

Question 3

What are good insulators and what do they depend on?

Answer 3

Good insulators have a low thermal conductivity. Energy transfer through them is very low. This depends on:
- The temperature difference across the material.
- The thickness of the material.

Question 4

How does the temperature of an object affect the infrared radiation it emits?

Answer 4

The higher the temperature of an object, the more infrared radiation it emits.
An object that has a constant temperature emits infrared radiation at the same rate it absorbs it.

Question 5

What is blackbody radiation?

Answer 5

The radiation emitted by a body that absorbs all radiation incident on it. A good absorber is a good emitter.

Question 6

Describe the method to carry out the thermal insulation required practical?

Answer 6

1. Set up equipment, wrapping 4 of 5 beakers with a different insulating material using rubber bands to secure it.
2. The beaker with no insulation is the control beaker.
3. Cut circles of cardboard to use as lids for each layer.
4. Fill each beaker with warm water from a kettle and record initial temperature of each.
5. Start stopwatch and measure temperature of water every 3 mins for 15 mins.
6. Calculate the overall change in temperature for each beaker.
   Can repeat varying the thickness of an insulating material.

Question 7

How does an object’s temperature increase?

Answer 7

If an object absorbs radiation faster than it emits it.
Shiny object emit less radiation than dark ones.

Question 8

What affects the temperature of the earth?

Answer 8

It depends on the rate that light/radiation from the Sun are reflected or absorbed and how much is emitted from earth.
Greenhouse gases absorb larger wavelength infrared radiation from earth to prevent it escaping and re emit it.

Question 9

What does the temperature rise of an object depend on?

Answer 9

The amount of energy supplied to it, the mass (greater mass decreases the rate it increases) and the material.

Question 10

What is specific heat capacity?

Answer 10

The energy needed to raise the temperature of 1kg of a substance by 1°C.

Question 11

What is the equation involving specific heat capacity?

Answer 11

Energy Transferred = Mass x Specific Heat Capacity (J/kg°C) x Temperature Change

Question 12

Describe the method to find the specific heat capacity of a material.

Answer 12

1. Set up equipment and wrap insulation around bases and sides of a 1kg metal block.
2. Place the thermometer and heater into each hole in the block.
3. Measure the initial temperature of the block.
4. Turn on power supply and start stopwatch.
5. Every 1 min for 10 mins, measure the voltage and current from the voltmeter and ammeter. Use the equation Energy = Voltage x Current x Time to find out the energy transferred and measure/record the temperature.
6. Switch off the power supply after 10 mins and allow to cool for around a minute before measuring and recording the final temperature.
7. Use the specific heat capacity equation to find the specific heat capcity.

Make sure voltmeter and ammeter initially set at zero.
Some heat will be dissipated to surroundings increasing shc.

Question 13

How could you reduce the rate of energy transfer in homes?

Answer 13

• Loft insulation reduces energy transfer through the roof.
• Cavity wall insulation reduces energy transfer through walls.
• Aluminium foil between radiator and wall reflects radiation away from the wall.
• Double glazed windows are thicker to reduce energy transfer.
• Solar panels absorb infrared radiation to generate electricity.