P1 - Energy for the Home

Question 1

What is heat?

Answer 1

Heat is a measure of energy among particles.

Question 2

What is temperature?

Answer 2

Temperature is a measure of the hotness, and usually a reflection of the energy in a substance.

Question 3

What is specific heat capacity?

Answer 3

The energy needed to raise 1kg of a substance by 1 degrees Celsius:

Energy = Mass * Specific Heat Capacity * Temp Change

Question 4

Why doesn’t the temperature of a substance change during changes of state (e.g. melting or condensing) even though more/less heat energy is being added?

Answer 4

If melting, intermolecular bonds are being broken. This absorbs/takes in energy, so the temperature doesn’t rise.

If condensing, intermolecular bonds are being formed/strengthened. This is an exothermic process, so energy is released; as a result, the temperature doesn’t change.

In other words, the energy consumed/released by bond forming or bond breaking cancels out the energy added/taken away externally.

Question 5

What is specific latent heat?

Answer 5

The amount of energy needed to melt 1kg of material without changing its temperature:

Energy = Mass * Specific Latent Heat

Question 6

Describe the conduction of heat energy.

Answer 6

Vibrating particles pass on extra kinetic energy to neighbouring particles.

Question 7

Why do metals conduct heat really well?

Answer 7

Metals have free/delocalised electrons that can move throughout the material. Heating gives these electrons kinetic energy, making them faster and more likely to collide with other electrons and to pass the energy. As the electrons are delocalised, this is a much faster transfer mechanism than waiting for vibrations to passed by ordinary neighbouring particles.

Question 8

Describe the convection of heat energy.

Answer 8

The more energetic particles move from the hotter region to the cooler region - taking their heat energy with them.

If a fluid is warmed, it becomes less dense and therefore rises. Once this warm fluid cools down, it becomes less dense and therefore begins to sink. A circulation known as convection current forms.

Question 9

Explain how convection currents can be eliminated.

Answer 9

You must create pockets of air, locations where the air cannot move, to prevent heat from being transferred. This can be achieved with clothes, blankets or cavity wall foam insulation.

Question 10

What are the best and worst absorbers of radiation?

Answer 10

Best = matt black
Worst = light-coloured, smooth and shiny

Question 11

Why are light-coloured and shiny surfaces the worst absorbers of radiation?

Answer 11

They are effective at reflecting electromagnetic waves, therefore they don’t absorb their energy.

Question 12

Explain an infrared oven or grill works.

Answer 12

The heat is radiated onto the surface particles of the food, and then travels to the centre of the food via conduction or convection.

Question 13

Explain how microwave ovens use radiation to cook food.

Answer 13

Microwaves penetrate around 1cm into the outer layer of the food and are absorbed by the fat and water molecules. The heat energy then travels, via conduction or convection, outwards from these heated molecules.

Question 14

How do you work out the efficiency of a process?

Answer 14

Efficiency = Useful Energy Output / Total Energy Input

Question 15

What is wave frequency?

Answer 15

The number of complete cycles or oscillations passing a given point per second.

Question 16

What is the wave equation?

Answer 16

Speed = Frequency * Wavelength

Question 17

What is the law of reflection?

Answer 17

Angle of Incidence = Angle of Reflection

Question 18

Explain how Total Internal Reflection occurs.

Answer 18

1. A light ray travels through a dense material (e.g. glass) toward a less dense material (e.g. air).
2. If the angle of incidence is greater than the critical angle, the ray reflects back into the material.

This is total internal reflection.

Question 19

What is diffraction?

Answer 19

Waves spread out when the pass through an gap or move past an edge.

Question 20

What factor effects the amount of diffraction?

Answer 20

The size of the gap relative to the wavelength of the wave. The wider the gap compared to the wavelength, the less diffraction that occurs.

Question 21

Explain the refraction of waves.

Answer 21

When a wave crosses a boundary between two materials of different densities at an angle, the wave changes diffraction.

This is because part of the wave enters the denser material first, slowing its speed before the rest of the wave. As a result, it changes direction.

Question 22

List the electromagnetic waves from largest to smallest wavelength.

Answer 22

Radio Waves
Microwaves
Infrared
Visible Light
Ultra Violet
X-Rays
Gamma Rays

Question 23

Explain how light is used to communicate via optical fibres.

Answer 23

Total internal reflection is achieved within a narrow tube. The light enters this tube at an angle greater than the critical angle, meaning that it doesn’t defract out of the tube and is instead totally internally reflected.

Question 24

What are the advantages of using light (via optical fibres) for communication?

Answer 24

Light is an electromagnetic wave, therefore, it travels extremely quickly.

Through multiplexing, lots of different signals can be transmitted at the same time.

It’s a digital signal, so there’s less interference.

Question 25

Describe the properties of light produced by a laser.

Answer 25

All waves in the laser beam are of the same frequency, meaning the light is monochromatic (it is just one colour).

The light waves are in phase, meaning the troughs and crests line up with eachother. They can be described as ‘coherent’.

They have low divergence - the beam is narrow and stays narrow, even at longer distances.

Question 26

How do CD players use lasers to read digital information?

Answer 26

The surface of the CD has a specific pattern of pits cut into it.

The laser is reflected slightly differently from within the pit compared to the other areas on the CD. The differences in these reflections can be picked up a sensor and recorded as electrical signals.

An amplifier or speaker can then convert the electrical signals into sound of the right frequency, loudness and pitch.

Question 27

How can we use IR to monitor temperature?

Answer 27

Hot objects give out heat radiation in the form of IR. The hotter an object, the more IR it releases.

As a result, we can use IR sensors to detect which objects are radiating the most IR - these can then be identified as the hottest.

Question 28

How can IR signals be used to control electrical equipment?

Answer 28

A device can emit a specific sequence of IR pulses to send to another device.

Each pulse represents a digital ‘on’ or ‘off’ code.

The receiving device can then decode this sequence of pulses and carry out the instructions.

Question 29

Describe the disadvantages of using IR signals to control electrical equipment?

Answer 29

You need to be close to the device.

The IR waves need to be directed straight at the receiver.

Question 30

Why do radiowaves travel well through the Earth’s atmosphere?

Answer 30

Radiowaves (and microwaves) have longer wavelengths, meaning they are not absorbed by the Earth’s atmosphere as much. This is also true for waves on the high-frequency end of the EM spectrum.

Question 31

What is the main advantage of using longer-wave radiowaves for communication?

Answer 31

They are able to diffraction around obstacles on the Earth, meaning you do not necessarily need a direct line of sight.

Question 32

How can the atmosphere help radiowaves travel around the earth?

Answer 32

1. The ionosphere is a layer of charged particles in the atmosphere. In this area, radiowaves travel faster - causing refraction.
2. When short-wave radio signals are reflected/bounced from the ionosphere and back down onto the surface. This is similar to total internal reflection.

Waves with a lower frequency are refracted most effectively back down onto Earth.

Question 33

What are the advantages of DAB (Digital Audio Broadcasting) over analogue audio?

Answer 33

1. There is less interference.
2. Through multiplexing, lots of different channels of audio can be broadcast at the same frequency. In the case of anologue signals, different channels may overlap and cause interference when using similar frequencies.

Question 34

What waves are used for satellite communication?

Answer 34

Microwaves

Question 35

Why are microwave transmitters/receivers usually positioned on hills?

Answer 35

Microwaves have a shorter wavelength than radio waves, meaning they don’t diffract around the curvature of the Earth. As a result, they need a direct line of sight - sending signals between hills is the best awy to achieve this.

Question 36

Mobile phone calls travel via which EM Wave?

Answer 36

Microwaves

Question 37

Why does the size of receiver depend on the size of the wave?

Answer 37

The receiver needs to be much larger than the size of the wavelength in order to minimise diffraction. The less diffraction that takes place, the less the waves are distorted - the less distortion, the clearer the signal.

Question 38

Why is better to have a larger telescope?

Answer 38

A higher resolution (clearer image) can be produced, since the telescope will much larger relative to the size of the wavelengths it receives. Because of this, there is less diffraction - therefore, the signals are clear and the resolution is higher.

Question 39

Explain, in terms of signal quality, why digital signals are better than analogue signals.

Answer 39

1. All signals, digital and analogue, weaken as they travel and therefore need to be amplified.
2. They all pick up noise and interference.
3. When you amplify these signals, the noise and interference is also amplified. However, because the digital signals only cover two defined values, it is much easier to remove the noise and interference from the signal.

Question 40

Why should pale-skinned people use sunscreen with a higher Sun Protection Factor (SPF)?

Answer 40

Pale skinned people absorb less UV radiation, meaning it is more likely the UV rays will begin to ionise and damage their skin cells.

Question 41

What does an SPF (Sun Protection Factor) of 15 tell the consumer?

Answer 41

The consumer is able to spend 15 times as long as they otherwise could in the sun without burning.

Question 42

How does the atmosphere protect us from UV radiation?

Answer 42

There’s a layer of Ozone (O3) high up up in the Earth’s atmosphere. Ozone is effective at absorbing UV radiation before it has a chance to hit the Earth’s surface.

Question 43

Why is there a hole in the Ozone layer of Antarctica?

Answer 43

The Ozone in the atmosphere began depleting as air pollution from CFCs began reacting with the ozone.

Question 44

Describe the properties and capabilities of P-waves.

Answer 44

• Longitudinal
• Travel through solids and liquids.
• Travel faster than S-waves
• They refract as density changes.

Question 45

Describe the properties and capabilities of S-waves.

Answer 45

• Transverse
• Travel through solids only (can’t travel through liquid outer core).
• Slower than P-Waves

Question 46

How can we use seismic monitoring (i.e. seismographs) to understand the Earth’s structure?

Answer 46

As S-waves can only travel through solids, we can identify the shadow areas left by these waves underneath the liquid outer core.

Furthermore, we can observe the sudden change in wave properties as P-waves refract through varying densities of material within the Earth.