Physics

Question 1

Describe what happens to wasted energy in energy transfers

Answer 1

Wasted energy is dissipated to the surroundings - usually as thermal energy due to friction.

Question 2

Explain some ways in which energy is transferred wastefully by mechanical processes.

Answer 2

During a mechanical process, energy is often wasted as thermal energy. This is due to friction, which generates this thermal energy - this is wasteful.

Question 3

How can we reduce wasted energy?

Answer 3

Lubrication, to reduce friction

Insulation, e.g to reduce heat escaping from a house

Question 4

How do you calculate wave speed?

Answer 4

frequency x wavelength

Question 5

Describe the differences between transverse waves and longitudinal waves

Answer 5

In transverse waves, particles vibrate at right angles to the direction of wave travel. Whereas, in longitudinal waves, particles vibrate parallel to the direction of wave travel.

Question 6

Give examples of transverse waves

Answer 6

EM Waves

Seismic S waves

Question 7

Give examples of longitudinal waves

Answer 7

Sound waves

Seismic P waves

Question 8

Describe differences in the ways parts of the EM spectrum are absorbed / transmitted

Answer 8

Visible light is absorbed by dark objects

Some EM radiation, eg UV radiation, is absorbed by the atmosphere.

Question 9

Describe why radio waves have a longer range than microwaves

Answer 9

Radiowaves have a much longer range as they are refracted in the ionosphere. This means that it can move around the Earth’s curved surface, without having to reflect of a satellite.

Whereas, microwaves aren’t refracted in the ionosphere, so to travel around the Earth they have to be reflected off a satellite.

Question 10

Explain what background radiation is.

Answer 10

Ionising radiation that is around us all the time from a number of sources.

Question 11

List some sources of background radiation

Answer 11

Radon Gas
Medical
Cosmic Rays
Buildings
Food and Drink
Nuclear

Question 12

Describe how a Geiger-Muller tube works

Answer 12

Radiation passing through the tube ionises gas inside it and allows a short pulse of current to flow. A GM tube can be connected to a counter, to count the pulses of current or the GM tube may give a click each time radiation is detected.

Question 13

Describe the process of B- and B+ decay

Answer 13

B- : In B- decay, an electron is emitted at high speeds from the nucleus. This is because a neutron has become a proton and an electron. Atomic number increases by 1, mass number stays the same

B+: In B+ decay, a positron is emitted at high speeds from the nucleus. A proton becomes a positron and a neutron. Atomic number decreases by 1, mass number stays the same.

Question 14

What happens during nuclear rearrangement after radioactive decay?

Answer 14

After radioactive decay, the nucleus has a lot of excess energy. It then loses this energy by emitting a high-energy gamma ray.

Question 15

What is half-life?

Answer 15

The amount of time taken for half of the radioactive nuclei in a sample of radioactive material to decay.

Question 16

What is the power of a lens?

Answer 16

A measure of how much the lens bends light rays passing through it. A more powerful lens bends rays more and has a shorter focal length.

Question 17

How do you calculate the power of a lens?

Answer 17

1/focal length

Question 18

What is the units for power?

Answer 18

dioptre

Question 19

Describe how the direction of a wave can change when moving into a different material

Answer 19

When moving into a new material, the wave can bend towards or away from the normal line.

Question 20

Explain some effects of refraction of light in terms of changing speeds

Answer 20

When moving into a more dense material, waves slow down, causing them to bend towards the normal line.
Whereas, when moving into a less dense medium, waves speed up causing them to refract away from the normal line.

Question 21

Describe what total internal reflection is

Answer 21

The reflection of a ray of light inside a medium when it reaches an interface

Question 22

What is the critical angle?

Answer 22

The angle of incidence which causes the angle of refraction to be 90 degrees, running along the boundary.

Question 23

Describe how ideas about the Solar System’s structure has changed over time

Answer 23

Ptolemy’s geocentric model - the idea that all planets revolved around us. They made observations using the eye and what they could see.

Copernicus introduced the heliocentric model.

Galileo then used the new telescope to discover 4 of Jupiter’s moons, plotting their movements to show that not everything revolved around the Earth.

Heliocentric model was now the widely accepted model.

Question 24

Describe how methods of observing the Universe has changed over time

Answer 24

At first, in Ptolemy’s time, observations were made using the naked eye.
The invention of the telescope allowed scientists to see objects in space in greater detail.
Photography allowed astronomers to make more detailed observations and measurements than were possible by drawings.

Furthermore, telescopes in orbit around the Earth gave us much clearer images and allowed us to detect different types of EM radiation that may have been absorbed by our atmosphere

Question 25

What’s the formula for work done?

Answer 25

force x distance moved in direction of force

Question 26

What two factors affect KE?

Answer 26

mass and velocity

ke = 1/2mv^2

Question 27

Describe how to measure the velocity of sound in a solid

Answer 27

Suspend a metal rod horizontally using clamp stands

Hit one end of the rod with the hammer, then use a
freequency app on a smartphone near the rod and note the peak frequency.

measure the length of the rod, the wavelength is 2x this
frequency x wavelength

Question 28

Describe how to measure velocity of water waves

Answer 28

Ripple Tank:
Set up a ripple tank with a straight dipper
Set up a ruler on an adjacent side
Vary voltage until you can always see 2 waves
Focus on a point, count how many waves pass in 10 seconds. /10 is your frequency.
Use ruler to estimate wavelength (see 10 waves, 10 is 5m, 1 wavelength is 0.5)

Buoy:
Measure the time taken for a wave to travel between two fixed points such as buoys. The speed is distance/time

Question 29

Why, even at constant speed, is the moon always accelerating?

Answer 29

Acceleration is defined as a measure of change in velocity.
Velocity is a vector quantity - considering both magnitude and direction.
The magnitude doesn’t change, but the direction does so velocity is constantly changing - therefore the moon is accelerating

Question 30

Describe the force needed to keep an object moving in a circular path

Answer 30

Centripetal force -a force that acts on a body moving in a circular path and is directed towards the centre around which the body is moving.

Question 31

Give some examples of a centripetal force

Answer 31

Moon - gravity directed towards the centre of the earth makes it move in a circular path

Question 32

Compare the penetrating and ionising abilities of alpha, beta and gamma radiation.

Answer 32

Alpha radiation is highly ionizing however can only travel a few centimeters in air and can be stopped by a piece of paper.

Beta radiation is moderately ionizing but is more penetrative than alpha, can travel a few metres in air and can only be stopped by a piece of aluminium.

Gamma radiation is weakly ionizing however is very penetrative and can travel a few km in air and is only stopped by thick lead or several metres of concrete.

Question 33

Describe advantages/disadvantages of internal radiotherapy

Answer 33

Advantages:
• Doesn’t always require surgery
• Higher total dose of radiation can be used to treat a smaller area and in a shorter time
Disadvantages:
• Surrounding tissue is more susceptible to mutations

Question 34

Describe advantages/disadvantages of external radiotherapy

Answer 34

Advantages:
• Tumor absorbs a lot of the energy
• Surrounding tissues are harmed as little as possible

Disadvantages:
• Only works if the cancer can be specifically targeted

Question 35

Explain how tracers are used in diagnosis

Answer 35

A slightly radioactive form of glucose can be put into the patient’s body. This travels to where respiration is occurring most rapidly - the radiation can then be detected by a gamma camera.

Question 36

Describe how a PET scanner works

Answer 36

A tracer that emits a positron is injected into the patient.

When this collides with an electron, both it and the electron are destroyed and two gamma rays are emitted in opposite directions.

The detector in the PET scanner moves around in the patient showing where different amounts of gamma radiation are coming from.

Question 37

Explain why isotopes for PET scanners have to be produced nearby

Answer 37

They need to have a short half-life so that other parts of the body are affected as little as possible. This means they lose their radioactivity very quickly so have to be produced nearby

Question 38

What is a chain reaction?

Answer 38

The sequence of fission reactions produced when a nuclear fission reaction triggers one or more further fissions due to releasing neutrons.

Question 39

Describe some uses of the short wave-lengths

Answer 39

UV is used in fluorescent materials - where they absorb UV radiation and re-emit it as visible light.

X-Rays can pass through many materials that others can’t. They can pass through muscles and fat easily but bone absorbs some X-Rays, making them useful in medical imaging.

Gamma rays transfer a lot of energy - so they are used to sterilise food and kill cancer in radiotherapy.

Question 40

Describe some uses of radiowaves

Answer 40

Radiowaves are used for transmitting radio broadcasts and TV programmes as well as other long-range communications. Some radio communications are sent via satellites.

Question 41

How are radio waves produced?

Answer 41

Radio waves are produced by oscillations in electrical circuits. Current moves up and down the aerial, oscillations cause radio waves to spread out from the aerial.

These can be absorbed by other aerials and cause oscillations in electric circuits connected to the receiving aerial

Question 42

Describe some uses of gamma rays

Answer 42

Gamma rays are able to transfer a lot of energy - so can kill cells. For this reason, they are used to sterilise food and surgical instrments by killing potentially harmful microorganisms.

Gamma rays are also used in cancer treatment and diagnosis.

When diagnosing with a medical tracer, a chemical that emtis gamma rays is put into the patient. This gamma radiation is detected using a gamma camera.

For treatment, gamma rays are used in external and internal therapy.

Question 43

What produces gamma radiation?

Answer 43

After radioactive decay, a nucleus has a lot of excess energy. It releases this energy as gamma radiation.