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Topic 7: Electric and Magnetic Fields (Quiz)
Terms in this set (48)
What happens to a charged particle in an electric field?
The charged particle will experience a force in an electric field
What is the force that a charged particle feels?
It is the electric field strength multiplied by the amount of charge on the particles in coulombs
What is the equation for the force experienced by a charged particle?
F = EQ
What is the equation for the energy transferred by a charge particle?
E = VQ
When does an electric field exist?
Between any objects which are at different electrical potentials
How can the strength of a uniform electric field be measured?
E = V/d
d = distance over which the potential difference exists
What are the two definitions of electric field strength?
E = F/Q
E = V/d
What are the two units used for electric field strength?
Why are lightning conductors spiked?
Charge is particularly concentrated in such regions - field is strongest here and the field lines are close together
Where there is a gap in the circuit?
At these points, the field may be felt, but conductive electrons are generally unable toe space their conductor and move across the gap - complete circuit is needed
How can charge be made to flow through an incomplete circuit?
With a capacitor
What is a fully charged capacitor?
p.d. across plates = p.d. of power supply
What is the unit of capacitance?
What factors do capacitance depend on?
- size of plates
- separation between the plates
- nature of the insulator
What is the name of the device used to measure the amount of charge?
What is the equation of capacitance?
C = Q/V
What is the role of a capacitor?
Store of electric potential energy
What is the equation for the energy stored in a charged capacitor?
E = 1/2QV
What does time constant indicate?
Time constant indicates how quickly a charged capacitor will discharge
Which factors mean that a capacitor will take longer to charge?
- greater resistance
- larger capacitance
How can a motor be made more powerful (faster)?
1. increase the current through the motor (I)
2. Increase the number of turns of the wire (l)
3. Increase the magnetic field within the motor (B)
F = BIl
F = BIl*sinx
By convention, which way does a field act?
Fields act from N to S by convention
What is a magnetic field?
A region of space which will cause a magnetic pole to feel a force is called a magnetic field
What are the units of magnetic flux density?
What are the units of flux?
What are the stages of mass spectrometer?
What is electromagnetic induction?
the production of an electromotive force (i.e. voltage) across an electrical conductor in a changing magnetic field.
How can a force be created with a stationary charge?
A magnetic field movie past a stationary charge will create a force - same as the force on a charged moving particle
What is the electromotive force?
the electrical intensity or "pressure" developed by a source of electrical energy such as a battery or generator
What is magnetic flux linkage?
The amount of magnetic flux interacting with a coil of wire - the product of the number of turns of the wire and the flux in that region
What are the units of flux linkage?
What is the equation of flux linkage?
flux linkage = BAN
What is Faraday's law of electromagnetic induction?
the magnitude of an induced e.m.f. is proportional to the rate of change of flux linkage
What is Lenz's law?
the direction of an induced e.m.f. is such as to oppose the change creating it
What is e.m.f. induction the result of?
E.m.f. induction is a result of the relative motion between a conductor (or coil) and the field due to a permanent magnet
Why is iron used as the core of a transformer?
It is very good at carrying magnetism
What type of current is used in a transformer and why?
Alternating current -the EM field produced is constantly varying so there will be a constantly varying induced e.m.f. in the secondary
What is the effect on a magnetic coil when the current through the coil alternates?
The force produced will reverse direction each time the current changes direction i.e. the coil will vibrate
For two current-carrying wires producing a magnetic field, what is the result of the force when the current in each wire is in the same direction?
The wires are attracted to one another
For two current-carrying wires producing a magnetic field, what is the result of the force when the current in each wire is in opposite directions?
The wires are repelled from one another
What are eddy currents?
a localized electric current induced in a conductor by a varying magnetic field.
What are eddy currents used for?
to create an electromagnetic field which opposes the turning magnet, resulting in a reaction force
for damping the movement of moving-coil meters e.g. ammeters and voltmeters so that the pointer moves smoothly to the correct reading rather than overshooting
When do eddy currents cause problems?
in motors, transformers and dynamos, which have coils which are wound on iron cores to increase the EM effect, but the iron metal also experiences flux. The eddy currents can cause a lot of heat in the iron
What is a galvanometer used for?
an instrument for detecting and measuring small electric currents
What happens when a bar magnet is pushed quickly into a solenoid (linked to a galvanometer) and then removed at the same speed?
Galvanotmeter pointer deflects as magnet moves in
Returns to zero as magnet stops
Deflects in the opposite direction
Same magnitude as magnet is removed
Why are eddy currents induced?
Due to changing flux or movement through a magnetic field
What is an application of eddy current?
inductive heating e.g. for melting metals
What is the purpose of the magnetic field in a cyclotron?
Force on (charged) particles at right angles to motion
Causes circular motion [not spiral / curved] OR force/acceleration is centripetal
THIS SET IS OFTEN IN FOLDERS WITH...
Units and Conversions (Physics)
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Topic 4: Materials (Quiz)
Topic 11: Nuclear Radiation
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