Which one of these statements is true about electricity and magnetic fields?
You always get a magnetic field when an electric current flows.
Under certain circumstances, it is possible to have an electric field flowing that does not produce a magnetic field.
Magnetic fields can never happen when electric currents flow.
Electric currents and magnetic fields have nothing at all to do with each other. Any appearance of either at the same time is entirely co-incidental.
The direction of the magnetic field around a single wire can be worked out using:
Fleming's Left Hand Rule
Faraday's Law
Lenz's Law
Screwdriver rule
What happens to the magnetic field if we increase the current going through a conductor?
The field lines spread out.
The field lines become more concentrated.
There would be no difference.
The field lines would disappear.
In an experiment to show the motor effect, a carbon rod is placed in the field of a strong magnet. It can roll freely on two brass rails. What happens when a current is passed through the carbon rod.
It is made magnetic and is attracted to the magnet.
It rolls along the brass rails.
Nothing
It bursts into flames.
In the experiment in question 4, the current is reversed. What does the carbon rod do now?
Nothing
It rolls in the same direction as before.
It rolls in the opposite direction as before.
It is made magnetic and is attracted to the other pole of the magnet.
In the same experiment as in question 4 (and 5), the magnet is turned so that the magnetic field is exactly parallel to the brass rails. What happens to the carbon rod?
It is made magnetic, and is attracted to whichever pole it's nearest.
It rolls down the track as it did before.
It splits in the middle, and one half rolls towards the magnet, and the other half away from the magnet.
It remains stationary.
What conditions have to be met for movement to occur in the motor effect?
There only needs to be an electric current.
There only needs to be a magnetic field.
There needs to be an electric current and a magnetic field at 90 degrees.
There needs to be an electric current and a magnetic field parallel with the electric current.
The direction of movement in the motor effect is determined by
Fleming's Left Hand Rule
Fleming's Right Hand Rule
Screwdriver Rule
Lenz's Law
A carbon rod is placed in a magnetic field. The rod is connected to a very sensitive voltmeter. Which one of these actions will make a voltage across the ends of the carbon rod?
The rod is left stationary.
The rod is moved towards the north pole of the magnet.
The rod is moved sideways along its axis.
The rod is moved towards the back of the magnet.
Which one of these will NOT increase the voltage across the ends of a conductor moved through a magnetic field?
Moving it faster
Adding more coils
Changing the material of the conductor
Making the magnet stronger.
An alternator is a generator that produces:
DC
AC
WC
H & C
A magnet is dropped into a coil. The voltage is measured. Which one of these actions will result in the voltage remaining zero?
Dropping the magnet in.
Pulling it out
Keeping it still
Moving it up and down.
The induction of a voltage by moving a wire in a magnetic field is the result of:
cutting field lines.
moving parallel to field lines.
soaking up the magnetism
connecting the magnet to an external electricity supply
Physicists say that cutting field lines results in:
a loss of flux
a gain of flux
a change in flux
an untidy mess of field lines all over the laboratory floor; it really should be done over the bin.
Which rule states: The potential difference induced is proportional to the rate of change of flux?
Lenz's Law
Fleming's Left Hand Rule
Principle of Conservation of Momentum
Faraday's Law.
Which one of these situations
describes Lenz's Law in practice?
A car hits a patch of ice and carries on in a straight line, instead of going round a bend.
A small petrol driven generator is being used to drive two demolition drills. As the drills come under load, the engine works harder.
Two cars collide and kinetic energy is turned into the noise and heat of the crash.
A matt black surface absorbs more infra red radiation than a glossy white surface.
Transformers have a laminated soft iron core. What is meant by this statement and what is the purpose of the lamination?
The core is a series of layers of soft iron, separated by layers of insulating varnish. The purpose is to reduce eddy currents
The core is a solid block of soft iron, surrounded by a layer of insulating varnish. The purpose is to reduce eddy currents
The core is a series of layers of soft iron, separated by layers of insulating varnish. The purpose is to increase eddy currents, thereby increasing the magnetism
The lamination is actually the manufacturer's label, supplying information to the engineer about the performance of the transformer.
Which one of these statements is true about the primary coil of a transformer?
The primary coil has no wire; when the wire is wound on, the coil is then known as a secondary coil.
Only the primary coil should be connected to the AC source.
Either coil can act as the primary.
The primary is connected to the load.
A voltage is induced in the secondary coil because:
the primary produces a very strong and steady magnetic field when connected to a battery.
the primary makes a constantly changing magnetic field when it's connected to an alternating supply.
the primary leaks electrons into the soft iron core, which travel to the secondary.
the primary is connected to the secondary by wires.
A transformer connected to a 240 V ac supply has a primary coil of 6000 turns. The secondary is 300 turns. What is the voltage from the secondary?
12 V
240 V
300 V
4800 V
A step up transformer is connected between the power station and the National Grid. Which one statement is correct about the step-up transformer?
In reduces both the voltage and the current.
It reduces the voltage and increases the current.
It increases both the voltage and the current
It increases the voltage but reduces the current.
Which one of these is the best reason for distributing electricity at very high voltages?
Thieves are deterred from stealing the cables.
The currents are reduced, so less energy is lost through the heating of wires.
The high voltages require engineers to show considerable ingenuity to solve the problems, and they rise to the challenge.
To stop children from climbing up the transmission towers (pylons) and making a nuisance of themselves,
The demand on the national grid
varies a great deal. Which one of these statements best explains how the electricity boards maintain a reliable supply during peak times?
Engineers watch TV and switch on pumped storage power stations during the adverts.
All power stations are kept working at full capacity all the time.
When lightning strikes the transmission lines, the extra electrical energy is harvested and stored.
The engineers switch on the wind farms.
During off-peak times, such as the early hours of the morning, there can be too much electricity in the national grid. How do engineers solve this problem?
Cutting off householders in rural areas.
Allowing some of the electricity to flow into huge storage tanks and lagoons, so that it's ready for the next period of peak demand.
Using the water turbines in pumped storage power stations as huge pumps to pump the water to the reservoirs in the hills.
Switching on some wind farms, so that the generators act as motors to turn the blades. The resulting breeze is often appreciated by neighbours on hot sticky nights.
Which one of these is the most likely fate of the Sun as it gets old?
It will go out suddenly, with a flash and a dull pop and blow all the fuses. It could even shatter.
It will grow to a red giant, then collapse to form a white dwarf, then a brown dwarf.
It will swell to a red supergiant and explode as a supernova. It will end up as a neutron star
It won't ever go out; it will shine for ever.
We have access to heavy elements like mercury and gold. The origin of these is thought to be due to:
the crushing forces that occurred when the Earth was being formed.
the cataclysmic event when a planetoid collided with the Earth to form a new Earth and the Moon.
cosmic dust from outer space that has been exposed to high energy radiation
material flung out in supernova explosions.
In its stable phase a star remains the
same shape. This is because:
the radiation pressure is balanced by the gravity of the star.
the radiation pressure is balanced by the electrostatic attraction between ions within the star.
the elements made from fusion form solid structures that run throughout the body of the star, holding it together.
charged particles are held in by the very strong magnetic fields of stars.
Which one of these is the explanation for the start of the Universe most favoured by astronomers today?
The universe never started at all. It has always been there, and always will be.
Material and energy leaked through a worm hole from a parallel universe.
A huge explosion called the Big Bang
None of these. The people who are putting about these theories don't know what they are talking about.
The process that keeps stars going is called:
oxidation
nuclear fussion
nuclear fission
nuclear fusion
Which process best describes the formation of stars and planets?
Gravity pulls the material together over millions of years.
Gravity repels the material so that it collects in corners of space.
The material clumps together because it's charged.
Wind in space blows the dust and gases. Where they block up worm holes, that is where stars are formed.