End of Topic test 21/03/24 Flashcards
Explain how the shaker torch is able to light the LED.
6 marks
- As the magnet moves through the coil, there’s change in magnetic flux linkage./Lines of magnetic flux cut by coil./Magnetic field lines cut by coil.
- E.m.f induced across the coil.
- This generates a current in the (capacitor) circuit.
- Diode only allows current in one direction.
- So the capacitor is charged (repeatedly).
- When the switch is closed, capacitor discharges through the LED.
Electrical transmission systems are used to transmit electrical power from place to place. Transformers are used to change potential differences (p.d.) and power transmission cables are used to transmit power.
The diagram shows a step-up transformer.
A step-up transformer is used to convert a lower p.d. to a higher p.d. An alternating p.d. is applied to the primary coil.
Explain how a higher p.d. is produced across the secondary coil.
4 marks
- A.C. in p coil produces changing magnetic flux.
- Magnetic flux is linked tothe secondary coil by the iron coil The changing magnetic flux induces an e.m.f in s coil.
- More turns on s coil
A device called a clutch can be used to connect a motor to a load. The diagram shows a design called an eddy current clutch.
Several magnets are embedded in the plastic disc and it is rotated by the motor
(i) Explain why a current is induced in the copper disc when the motor is switched on.
(ii) Explain, using Lenz’s law, why the copper disc rotates.
2, 3 marks
i)- Change in magnetic flux
- Due to Faraday’s Law, there is an induced e.m.f.
ii)- Copper disc rotates in same direction.
- beacuse it reduces rate of mag flux change.
- so as to oppose the change that produces it.
V IN is applied to a diode and resistor as shown.
The p.d. across the resistor is VR and the p.d. across the diode is V D. V D is the output.
Explain why V IN = V R + V D at any given time.
2 marks
- Energy is conserved/Kirchoff’s Law.
- So the sum of p.d. s in a series circuit must equal the e.m.f applied.
A teacher carries out a demonstration to illustrate the laws of electromagnetic induction. She uses three tubes of identical dimensions. One is made of plastic, one copper and one copper with a slit cut into its length. The teacher suggests that the magnet would take longer to fall through the copper tube as a consequence of the laws of electromagnetic induction.
Assess the validity of this suggestion.
6 marks
- When the magnet falls, there is a rate of change of mag flux linked with the tube.
- The change in flux linkage for the copper tube induces an emf.
- The induced emf causes a current to flow in the tube.
- the induced emf (and current) are in such direction that opposes the change in flux linkage.
- A force is exerted on the magnet opposing its motion.
- Plastic is not a conductor so no current is induced. Shorter time than the copper tube. Teacher is correct
A teacher carries out a demonstration to illustrate the laws of electromagnetic induction. She uses three tubes of identical dimensions. One is made of plastic, one copper and one copper with a slit cut into its length.
Before the teacher releases the magnet through the copper tube with a slit along its length, she asks the class to consider how the time taken will compare with the time for the other copper tube. The class predicts that the time will be the same.
Explain, using electromagnetic induction, whether this prediction is correct.
3 marks
- Slit will limit the size of current induced.
- Smaller force opposing the magnet.
- Less time taken for the magnet to fall.
Proton beam therapy is being introduced in the UK as a new cancer treatment.
A beam of protons is accelerated by a cyclotron to an energy of 23 MeV and is then focused onto a tumour.
Explain how the cyclotron produces the high-energy proton beam.
6 marks
- There is an alternating p.d/e field.
- P.d/e field accelerates protons between the dees.
- M field perpendicular to the plane of dees.
- Proton’s path curved by m field.
- As velocity of protons increases, radius of the paths in the dees increases.
- Time for a proton in a dee is the same/the frequency of p.d/e field is constant.
Identical bar magnets are suspended from identical springs, with the North pole of each
magnet inside a coil of wire as shown. The two coils are connected together with conducting
leads.
Magnet A is displaced so that it oscillates vertically. The North pole of magnet A moves into and out of the coil of wire with simple harmonic motion. As this motion continues, magnet B starts to oscillate. The amplitude of oscillation of magnet B increases over time.
Explain why magnet B starts to oscillate with an increasing amplitude.
6 marks
- As magnet A moves, its coil experiences a change in m flux (linkage)
- Emf induced
- The induced emf causes current to flow in both coils.
- Current in second coil causes a force on magnet B. Setting it into oscillation.
- Same period and frequency for both systems.
- Resonance occurs.
The diagram shows the inside of an electric toothbrush and a charger.
The charger contains a coil wrapped around an iron core. The coil is plugged into the mains a.c. supply.
The toothbrush also contains a coil that sits around the iron core when the toothbrush is placed on the charger to recharge the battery of the toothbrush.
Describe how the charger is able to charge the low-voltage battery.
6 marks
- The supply creates a changing magnetic field in the iron core.
- Rate of change of flux in toothbrush coil is equal to the rate of change of flux in the charger coil.
- The changing flux linkage in the coil of the toothbrush induces an emf due to Faraday’s law.
- E= -dNΦ/dt, to step down the emf, there must be fewer turns in the coil.
- Emf in toothbrush coil must be larger than the toothbrush battery.
- Diode, so the battery is not discharged by the alternating emf.
The diagrams show the plan view and side view of a moving coil ammeter.
The coil within a very sensitive moving coil ammeter can be damaged when the ammeter is transported. The two ends of the coil are connected together when the ammeter is transported. This reduces the movement of the coil and makes it less likely to be damaged.
A student suggests that this is due to Faraday’s law and Lenz’s law.
Explain how these laws apply to this situation.
4 marks
- Change of flux when the meter is moved.
- Emf induced which will produce a current. (Faraday’s).
- Current-carrying conductor within a magnetic field experiences a force.
- These forces opposes the coil’s motion. (Lenz’s)
Hybrid electric vehicles (HEV) use the same device both as a generator to charge the car battery and as an electric motor to support the propulsion system. A simplified diagram of the device is shown. The coil can rotate freely around the axis.
Describe how the device can be used as both a generator and an electric motor.
6 marks
Generator:
1. Coil has to be rotated.
2. Cuts magnetic flux.
3. Emf induced.
Motor:
1. Current provided to coil.
2. Force on sides of the coil that are perpendicular to the m field.
3. Rotate coil as forces provide a momentum.
A simple electric motor consists of a coil that is free to rotate in a magnetic field.
A student connects the motor to an ammeter and a battery.
The graph shows how the current I in the coil varies with time t. The switch is closed at time
T.
Explain why the current rises to a maximum then decreases.
Your answer should include a reference to Faraday and Lenz’s laws.
6 marks
- max/initial current is equal to battery emf divided by R (V=IR).
- coil rotates.
- coil cuts magnetic flux.
- emf induced (Faraday’s)
- Opposes original emf/current due to Lenz’s law.
- Faster the coil rotates, larger the backward/opposing emf.
Describe the characteristics of a main sequence star.
2 marks
- mainly converts hydrogen to helium in the core/hydrogen burning.
- maintians a constant luminosity.
In 2016 the Breakthrough Starshot initiative was announced. This project intends to send a fleet of small probes to Proxima Centauri, the nearest star to the Sun. This journey would take about twenty years.
Describe how the distance to nearby stars like Proxima Centauri is determined.
3 marks
- the star is viewed from two positions at 6 months apart.
- the change in angle of the star against backdrop of fixed stars is measured.
- trig is used to calculate the distance.
A Hertzsprung-Russell (HR) diagram shows how the luminosity L depends on the surface temperature T for a group of stars.
The HR diagram below is for a young star cluster.
Explain how we can tell that the young star cluster is in the early stages of its evolution.
2 marks
- All the stars are in the main sequence belt.
- In older clusters there would be red giant stars.
The diagram shows the spectra produced by two stars. Spectrum A is produced from the light from the Sun and spectrum B is produced from the light from a distant star.
The dark lines are produced when light from the core of the star is absorbed by hydrogen atoms in the outer regions of the star. Light is then re-radiated, but in all directions, giving rise to the dark lines in the spectrum.
Explain why the long wavelength lines are shifted by a greater amount than the short wavelength lines.
2 marks
- the fractional change in wavelength is proportional to the relative volicity of the source.
- hence the change in wavelength is proportional to the wavelength.
The diagram shows the spectra produced by two stars. Spectrum A is produced from the light from the Sun and spectrum B is produced from the light from a distant star.
The dark lines are produced when light from the core of the star is absorbed by hydrogen atoms in the outer regions of the star. Light is then re-radiated, but in all directions, giving rise to the dark lines in the spectrum.
One of the lines in the hydrogen spectrum occurs at a wavelength of 656 nm in the laboratory.
Explain what conclusion can be made from the shift in wavelength of this line in spectrum B. Your answer should include a calculation.
4 marks
- work out shifted wavelength.
- Δλ/λ = v/c
- v = …..
- star is moving away from Earth
In 2016 astronomers announced the discovery of an Earth-like planet orbiting Proxima Centauri, the closest star to the Sun.
The planet was detected because of the small movement of the star as the planet orbited. The movement was detected using the Doppler shift in the frequency of light travelling to the Earth.
The graph shows how the component of the star’s velocity v towards the Earth varied over time.
Explain how the Doppler shift was used to obtain the data shown on the graph.
4 marks
- freq/wavelength emitted by star measured.
- find difference between this and lab emissions.
- Δλ/λ = v/c
- if positive, freq has increased. if negative, freq has decreased.
The graphs below show plots for data collected in 1929 (Figure 1) and 1931 (Figure 2).
The data used by Hubble for his 1929 plot (Figure 1) is contained within the rectangle close to the origin of the 1931 plot (Figure 2).
Explain how Hubble’s observations support the conclusion that the universe is expanding, and assess the reliability of this conclusion on the basis of Hubble’s original data.
5 marks
- wavelength change bigger when galaxies are further away.
- the further the galaxy is, the faster its moving. moving away from each other. universe expanding.
- large amount of scatter in original data set.
- original data set covers smaller data range.
- hence, based on the original set of data, the conclusion made by hubble was quite speculative.
