# OCR Physics A FFFP

?
Define Magnetic Flux
Magnetic Flux is the magnetic flux density x area perpendicular to field direction.
1 of 22
Explain why the magnitude of the magnetic flux through the coil varies as the coil rotates
The area changes relative to the field direction and is maximum when field is perpendicular to B
2 of 22
State Faradays Law of electormagnetic induction
Faradays Law of Electromagnetic induction states that the induced e.m.f. is proportional to the rate of change of magnetic flux.
3 of 22
Describe and Explain the variation with time of the induced. e.m.f across the ends of the coils.
e.m.f. is max when ᵩ is zero, and e.m.f is zero when ᵩ is max. They both have the same frequency.
4 of 22
Define Capacitance.
Capacitance is charge per unit potential difference
5 of 22
The energy stored in the capacitor decreases to zero. State where the initial energy stored in the capacitor is dissipated.
The energy is dissipated into heat.
6 of 22
Olbers Paradox is based on two assumptions about the nature of our universe. State these two assumptions.
It is of uniform density (static) and there is an infinite number of stars.
7 of 22
Describe how the fate of the Universe depends on its average density
Above critical value = It will contract. Less than critical value = will continue to expand forever. Close to Critical Value = Expand towards a limit.
8 of 22
Describe one advantage and disdvantage of MRI
ADVANTAGE: Gives better soft tissue contrast. DISADVANTAGE: Takes a long time to complete
9 of 22
Explain why the activity of a radioactive material is a major factor when considering the safety precautions in the disposal of nuclear waste.
If the material has a long half life, it will remain active for longer and hence needs a long term disposal option.
10 of 22
Name the force responsible for Beta Decay
The Weak Force
11 of 22
Two protons fuse together. Explain how the protons are able to remain together.
Due to the Strong Force
12 of 22
Explain why the proton must have a very large velocity for the fusion to occur and the protons to remain together.
As the proton moves towards the stationary proton, it experiences a repulsive force that slows it down. It needs the high velocity to get close enough for the short range strong force to have an effect.
13 of 22
State and describe one way in which X-ray photons interact with matter.
The photoelectric effect where an electron is ejected from an atom and the atom is ionised.
14 of 22
Explain how image intensifiers are used to improve the quality of the X-ray image. Explain clearly the process involved which makes the image brighter.
A photon releases an electron, which is accelerated onto a fluorescent screen. The number of electrons is increased. An intensifier converts X-ray photons into an increased number of visible photons.
15 of 22
The seperation between the plates is doubled but the p.d. across the plates is kept the same. Explain how this would affect the gain of an electron when moving between the plates.
There would be no change in the gain of the KE, as KE = VQ and doesnt depend on distance.
16 of 22
The farad is the number of coloumbs per volt.
17 of 22
Explain how the plates of the capacitor become charged in terms of the movement of charged particles in the circuit
The electrons flow clockwise (from negative to postive). They are placed onto plate A and removed from plate B
18 of 22
Explain the effect on the initial rate of discharge of the capacitor when a second resistor of resistance 3.7MΩ is connected in parallel with the initial resistor.
The resistance of the circuit is halved, hence rate of discharge is doubled.
19 of 22
Explain why the magnetic field does not change the speed of the protons
The force is proportional to the velocity, no work is done.
20 of 22
State Hubbles Law
The speed of recession of a galaxy is proportional to its distance from Earth.
21 of 22
Describe two observations that directly support the idea of the big bang.
The more distant galaxies are moving faster than the closer galaxies, and the existence of background microwave radiation.
22 of 22

## Other cards in this set

### Card 2

#### Front

Explain why the magnitude of the magnetic flux through the coil varies as the coil rotates

#### Back

The area changes relative to the field direction and is maximum when field is perpendicular to B

### Card 3

#### Front

State Faradays Law of electormagnetic induction

#### Back ### Card 4

#### Front

Describe and Explain the variation with time of the induced. e.m.f across the ends of the coils.

#### Back ### Card 5

#### Front

Define Capacitance.

#### Back 