P2 - Energy Transfer by Conduction

Question 1

What is Specific Heat Capacity ?

Answer 1

Specific Heat Capacity is the amount of energy required to raise the temperature of 1kg of the substance by 1°C

Question 2

Specific Heat Capacity Equation

Answer 2

∆E = m * c * ∆0

change in thermal energy (J) = mass (kg) *specific heat capacity (J/kg °C) * temperature change (°C)

Question 3

J -> kJ?

Answer 3

divide by 1000

Question 4

reminder:

Answer 4

only rearrange an equation after putting the numbers in, to show you know what goes where.

Question 5

There are two factors of how quickly a building loses thermal energy. What are they?

Answer 5

• Thermal Conductivity
• How thick the walls of a house are

The higher the thermal conductivity, the higher the rate of energy transfer by conduction. – Double glazed windows and insulated walls and ceilings have low thermal conductivity and keep in heat, saving money.

Question 6

Describe the specific heat capacity practical.

Answer 6

1. Place the beaker on a balance and press zero.
2. Add oil to the beaker and record mass of oil.
3. Place a thermometer and an immersion heater into the oil. Read starting temp of oil.
4. Wrap the beaker in insulating foam to reduce the thermal energy transfer to the surroundings.
5. Connect a joulemeter (and a power pack) to the immersion heater you place in earlier.
6. Leave oil for 30 minutes.
7. Read the number of joules of energy that passed into the immersion heater and the final temperature of the oil.

Now you have all the info needed to calculate the SHcapacity of the oil.

Question 7

Why would the SHC practical possibly be inaccurate?

Answer 7

• Thermal energy could pass into the air. ⇾ Use an insulator with a lower thermal conductivity.
• Not all thermal energy passes into the oil ⇾ ensure immersion heater is fully submerged
• Incorrectly reading the thermometer ⇾ use an electronic temp probe
• Thermal energy not being equally spread through oil ⇾ stir the oil

Question 8

Describe the Thermal Insulation practical.

Answer 8

Start by comparing the effectiveness of different materials as thermal insulators:
1. Place a small beaker into a larger beaker
2. Boil some water ⇾ transfer 80cm of it to the smaller beaker
3. Use a piece of cardboard as a lid for the larger beaker (must have a hole for a thermometer to go in. the thermometer needs to be in the hot water.)
4. Record the starting temperature of the water and start a stopwatch.
5. Record the temp of the water every 3 minutes for 15 minutes.
—–
Pour out the hot water and repeat steps 2–5 but have an insulating material like bubble wrap to fill the gap between the small beaker and larger beaker.
Test this with different insulators and have the same mass of each insulator.

Record in a table or graph.

Question 9

What is Black Body Radiation?

Answer 9

A perfect black body absorbs all radiation and is the best possible emitter of radiation.

If an object is warmer than it’s surroundings, it will emit more radiation than it absorbs. The reverse is also true (a cooler object absorbs more radiation than it emits). If an object is at a constant temperature, it is absorbing and emitting radiation at the same rate.

Question 10

How does the earth gain or lose energy.

Answer 10

Through absorbing radiation from the sun (some radiation is simply reflected by the clouds) and emitting radiation into space (some is trapped by gases such as CO₂)

Human activity is increasing the amount of radiation trapped on earth through greenhouse gases. Also, some radiation attempting to escape our atmosphere can be reflected back by clouds.

Question 11

What are the 3 ways

things increase their thermal energy store? (temperature)

Answer 11

• Radiation (for empty space)
• Conduction (for solids)
• Convection (for fluids)

Question 12

How does conduction work?

Answer 12

Vibrating particles transfer energy to neighbouring particles.

how well objects transfer energy by conduction is known as their ‘thermal conductivity’

Question 13

What is the thermal conductivity of

Metals, fluids and plastics?

Answer 13

• Metals ⇾ high
• Fluids ⇾ low
• Plastics ⇾ low (used as insulators)

Question 14

What does ‘fluids’ refer to?

Answer 14

Liquids and gases.

Question 15

How does convection work?

Answer 15

When heating a fluid, the warmer part expands towards the cooler area and is less dense (rises above cooler particles ⇾ then the cooler particles warm up while the warmer particles cool down and the cycle repeats. ⇽ this is a ‘convection current’)

Question 16

How to reduce convection?

Answer 16

Stop the free flow of fluids.

Question 17

How does radiation work?

Answer 17

Heat energy travels through infrared waves. The hotter an object, the more radiation it’s emitting.

Question 18

Internal Energy

Answer 18

The total energy stored by the particles making up a substance or system.

Question 19

Kinetic Energy Store

Answer 19

The energy an object has because it’s moving.

When KES increases, temperature increases and internal energy increases. The higher the temp, the higher internal energy.

The amount of energy to increases the temperature is the specific heat capacity.

Question 20

As the temperature increases so does the intensity of…

Answer 20

The intensity of every emitted wavelength increases and the intensity of shorter waves length increases too. (hence why blue fire is hotter than orange fire, because blue fire has shorter wave lengths and is therefore hotter)