Electricity and magnetism Flashcards
How do you work out power?
Power=current X voltage
How do you work out I?
I means current
Current = power/voltage
What is the units for charge
Coulombs C
How to work out resistance?
Resistance= voltage/current
What is the units for resistance?
Ohms
How do you work out energy in circuits?
Energy= power X time (s)
What is current measured in?
Amps
What is a fuse and why is it important?
A fuse is a thin piece of wire which is designed to melt if the current flows for it is too high
A fault in a circuit might cause a large current
This may damage the device or start a fire
A fuse is to prevent this from happening
What is a magnet
Magnets have a magnetic field that exert a force onto another body that has magnetic properties
What are the types of magnets
Permanent magnet- always has a magnetic field
Temporary magnet- becomes magnetic under domain influence. Under influence of another magnet
What are the types of magnetic material?
Ferromagnetic- e.g iron, retains magnetism
Paramagnetic- e.g copper, low permeability
Gadolinium is used in MRI to improve images
Dramagnetic- No magnetism
What is domain theory?
Domains are areas in the magnet that align in order for the substance to be magnetic
So in substances that don’t have domains aligned they aren’t magnetic
-however some substances can have their domains with other magnets.
What affects the magnitude of force?
Propertional- strength of the magnets
Inversely proportional to the distance squared (the further away the weaker the force)
What are the units of magnetic field strength or magnetic flux density?
Measured in Gauss (G) (Not SI units)
Or Tesla (T) (SI units)
How many Gauss’s equal 1 Tesla
1 Tesla= 10,000 Gauss
How can magnetic fields arise?
Magnetic fields can arise due to current carrying conductors
As electrons flow a magnetic field will be generated around a electric wire
What is Lenz’s law?
And what can it cause?
The induced EMF is in the opposite direction to what caused it
This leads to power loses as the current generated is inhibited by the magnetic field as it opposes it
What does EMF stand for?
EMF- electromotive force is similar to potential difference
What are the principals of magnetive?
Generator effect
Motor effect
What are the electromagnetic laws?
Faraday’s laws
What is the generator effect?
…..
Similar to motor effect execpt in reverse
What is the motor effect?
Example
Coil of wire placed in a magnetic field, so when the current flows it creates a MF that opposes the first MF, which causes the coil to rotate. The rotation/movement can drive devices.
For Example, an induction motor spins the anode on the x-ray tube.
What are the Faraday’s laws?
….
What the influence of sharp objects on electric field?
And how to prevent it?
Charge collect around the surface of a object and sharp edges will have a higher concentration of charge.
This can result in electrical shock
To prevent this -earth them, no sharp edges
What does current mean?
The number of electrons
What’s another word for voltage?
Potential difference
What does resistance mean and factors that effect it?
Resistance means that electrons are prevented from flowing
Heat increases resistance
Thin wires have more resistance
And thick wires have less resistance as electrons can flow more easily and heat up less quickly
What does potential difference mean?
Potential difference (voltage) is the driving force, However current is the flow of electrons so in none circuits there is potential difference
But in circuits there is a flow of electrons
What measure of current would you use in rad?
In rad milliamps (1mA=0.001Amp
What is a semi- conductor
Semi-conductors permit the flow of electrons in one direction only (used to regulate flow in a circuit) e.g silicon
What’s the units for power?
Watts
What’s the units for energy?
Joules
What is a solenoid?
Solenoid refers to a soft iron being used in the coil to strengthen the magnetic field
Current creates a magnetic field in the wire and the soft iron enhances it
Why is electricity needed in an x-ray tube?
To cause electrons to be released from the cathode
To drive electrons to the anode for photon production
What are the types of electrical current?
Direct current (D.C) Alternating current (A.C)
What does direct current mean?
Flows in one direction does not change in direction when it reaches its peak
What does alternating current mean?
Changes in direction but it reaches it’s peak
What does Faraday’s law of electromagnetic induction mean?
When a conductor is placed in an changing magnetic field EMF is induced and if the conductor circuit is closed current is also induced.
Changing magnetic field induces alternating current.
What device is used to get direct current from alternating current
Commutator (split ring) is used
How does a step-up transformer work
If there is more coils in the secondary coil than the primary coil it steps up the voltage.
How does a step-down transformer work?
If there is less coils in the secondary coil than the primary coil it steps down the voltage.
What does a rectifier do?
Converts alternating current to direct current.
How does a transformer work
It steps up or step downs the voltages
The changing magnetic field induces in the secondary coil
This is mutual induction
