Electric and magnetic fields

Question 1

what is a force field?

Answer 1

a force field is where an object experiances a non contact force

Question 2

what is an electric field?

Answer 2

this is a force field where a charged particle experiences a force

Question 3

what is the equation for electric field strength?

Answer 3

E=F/Q
F=force exerted on object

Question 4

What is the equation for electric field strength in a radial field?

Answer 4

E=Q/4πε0r^2

Question 5

what is coulombs law?

Answer 5

F=Q1Q2/4πε0r^2

Question 6

what are point charges

Answer 6

this is a charge in a single point in space

Question 7

what do point charges form?

Answer 7

radial electric fields

Question 8

what is the equation for a point charge?

Answer 8

E=Q/4πε0r^2

Question 9

What is absolute electric potential?

Answer 9

electric potential energy is what a charge gains when it is placed in an electric field

Question 10

where is the absolute magnitude of electric potential greatest and how does this change as distance is increased?

Answer 10

It is greatest at the surface and as distance increases the electric potential decreases, so electric potential at infinity = 0.

Question 11

how is force exerted in uniform and radial fields?

Answer 11

In a uniform field the same electric force is exerted everywhere. In a radial field the magnitude of force exerted depends on the distance from each of the charges

Question 12

What are equipotential surfaces?

Answer 12

In a uniform field these are lines parallel to the magnet. On a point charge they form concentric circles. Here a charge moving on the surface experiences no work. They are equally spaced

Question 13

what is capacitance?

Answer 13

the charge stored by a capacitor per unit p.d.

Question 14

how can you find the energy stored by a capacitor from a Q/V graph?

Answer 14

The area underneath the. graph

Question 15

how can you use a data logger?

Answer 15

to find values of I and V simultaneously, allowing you to plot I/t and V/t graphs.

Question 16

what happens when a capacitor is connected to a power supply and charging?

Answer 16

I flows
-ve charge builds up on plate connected to -ve terminal
electrons are repelled by the -ve charge on that plate so they move to the +ve terminal.
an equal but opposite charge is formed on each plate this creates a p.d
as the Q across the plates increases the p.d also increases but the electron flow will decrease due to electrostatic repulsion, therefore I decreases until it reaches zero.

Question 17

what happens when a capacitor discharges?

Answer 17

-I flows
-Q,I and p.d will all fall exponentially, so they will all take the same amount of time to halve.

Question 18

what is the time constant (RC)?

Answer 18

RC which is resistance x capacitance.
when discharging a capacitor the value of RC is 0.37 of its initial value.
when charging a capacitor the RC value is 0.63 of its maximum value.

Question 19

how can you find the value of RC on graphs?

Answer 19

I/t, Q/t, V/t by finding the time where the values are either 0.37 of the initial value when discharging or 0.63 of the max value when charging.

Question 20

what is magnetic flux density (B)?

Answer 20

This is the measure of strength of the field and it is measured in tesla (T).

Question 21

what is magnetic flux (Φ)?

Answer 21

this describes the magnetic field of magnetic field lines passing through a given area.

Question 22

what is magnetic flux linkage?

Answer 22

B x the number of turns on a coil N

Question 23

what happens when a charged particle moves through a magnetic field?

Answer 23

It experiences a force perpendicular to the direction of motion.

Question 24

how is emf induced in a coil when there is relative motion between the coil and a permanent magnet?

Answer 24

when a conducting rod moves relative to a magnetic field, the electrons in the rod will experience a force and build up on one side of the rod inducing a emf.
This is electromagnetic induction.
This also happens when you move a bar magnet relative to a coil of wire.

Question 25

what is faraday’s law?

Answer 25

the magnitude of an induced emf is equal to the rate of change of flux linkage.

Question 26

what is lenz’s law?

Answer 26

the direction of induced current is such as to oppose the motion causing it

Question 27

How is lenz’s law demonstrated by a magnet falling through a coil of wire?

Answer 27

As the magnet approaches the coil there is a change of flux through the coil, so an emf and current is induced.
The same pole of the magnet is induced in the coil to repel the magnet causing the magnet to slow down.
In the centre of the coil there is no change in flux so no induced emf.
As the magnet leaves the coil, the opposite pole of the magnet is induced so it is attracted and slowed.

Question 28

How does lenz’s law link to the conservation of energy?

Answer 28

Lenz’s law ensures that the electrical energy gained by induction of current, is equal to the amount of energy being removed.

Question 29

what is the peak value?

Answer 29

The lowest or highest distance from the equilibrium point

Question 30

what is root mean square (rms)?

Answer 30

the average of all squares of the possible values. This makes it so the negative and positive don’t cancel out and an effective value for I/V output is given.

Question 31

what is time period?

Answer 31

the time taken to complete one full cycle

Question 32

what is frequency ?

Answer 32

the number of complete oscillations passing through a point per second

Question 33

How is emf induced in a coil by the change of current in another coil linked to this coil?

Answer 33

a magnetic field is induced around a current carrying coil.
If current changes, magnetic field will also change, so if there is a second coil in the magnetic field when it changes a current will be induced in it
This is mutual inductance.
The induced emf in the second coil is proportional to the change in current in the first coil