electric and magnetic fields

Question 1

force field

Answer 1

a force field is an area in which an object experiences a non-contact

Question 2

electric field

Answer 2

a force field in which charged particles experience a non-contact force

Question 3

electric field strength

Answer 3

force per unit charge experienced by an object in a field
E=F/Q

Question 4

coulombs law

Answer 4

the magnitude of force between two point charges is proportional to the product of their charges and inversely proportional to the square of the distance between them

Question 5

electric field strength in a radial field equation

Answer 5

E=KQ/r^2

Question 6

electric potential

Answer 6

potential energy per unit charge of a positive point charge at that point in the field

Question 7

where is the magnitude of electric potential maximum

Answer 7

at the surface of the point charge

Question 8

where is the magnitude of electric potential smallest

Answer 8

it is 0 at infinity

Question 9

electric potential in a radial field equation

Answer 9

V=KQ/r

Question 10

electric potential difference

Answer 10

energy needed to move a point charge between two points

Question 11

what does the distance between field lines represent

Answer 11

the strength of the field at that point

Question 12

capacitance

Answer 12

charge per unit potential difference stored in a capacitor

Question 13

how can you find the energy stored by a capacitor in a charge-potential difference graph

Answer 13

energy will be the are underneath the graph

Question 14

how do capacitors charge once a switch is closed

Answer 14

-current starts flowing and negative charge builds up on the negative terminal plate.
-on the opposite plate, electrons are repelled by the build up of negative charge on the plate, therefore these electrons move to the positive terminal and an equal but opposite charge is formed on each plate, creating a potential difference.
-as the charge increases, so does the potential difference, but electron flow decreases due to the repulsion, so current eventually becomes zero.

Question 15

capacitor discharge

Answer 15

the current flows in the opposite direction. electrons transferred to the positively charged plate through the resistor. the current, charge and potential difference fall exponentially

Question 16

time constant

Answer 16

value of time taken to:
-discharge a capacitor to 37%
-charge a capacitor to 63%

t=RC

Question 17

magnetic flux density (B)

Answer 17

strength of the magnetic field, measured in Teslas

Question 18

magnetic flux (Φ)

Answer 18

magnetic field lines passing through a given area
Φ=BA

Question 19

Magnetic flux linkgage

Answer 19

magnetic flux multiplied by the number of turns in the coil, N.
NΦ=NBA

Question 20

charged particles moving in a magnetic field

Answer 20

they experience a force, F=BqV. the direction if the force can be found by using lemmings left hand rule, the force is alway perpendicular to the motion of travel, which causes charged particles to follow a circular path as it acts as a centripetal force.

Question 21

current carrying conductor in a magnetic field

Answer 21

when a current flows through a wire, a magnetic field is produced. therefore when this wire is in a field, it experiences a force, F=BIL

Question 22

induction of emf in a coil

Answer 22

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 , causing an emf to be induced. known as electromagnetic induction.
if the coil forms a complete circuit, a current is also induced

Question 23

two laws which govern electromagnetic induction

Answer 23

-faradays law:the magnitude of induced emf is equal to the rate if change of flux linkage
-lenzs law: the direction of induced current is such that it oppose the motion causing it

Question 24

factors affecting the emf induced

Answer 24

-number of turns in the coil
-magnetic flux density
-area of the cross section
-time taken for the motion

Question 25

induction of emf in a coil through the change in current of another coil

Answer 25

magnetic field is induced in a current carrying coil. if the current through the wire changes (alternating current), the magnetic field will also change, which will induce an emf in the other coil if it is within the magnetic field. this is called mutual inductance. the emf in the second coil is proportional to the change in current in the first coil.

Question 26

example of mutual inductance

Answer 26

transformer

Question 27

factors influencing the emf induced in the second coil

Answer 27

-magnetic flux density (B) of the field created by the initial coil
determined by the number of turns in the coil
-the distance between the coils
further apart means less magnetic flux passed on
-number of turns (N)
-area of cross section (A)
-time taken for change in current

Question 28

how can lenzs law be shown

Answer 28

1) magnet falling approaches coil, causes a change in flux and so an emf is induced
2) due to lenzs law, the current opposes the motion, so the same pole as the pole of the magnet approaching will be induced which repels the magnet and slows the magnet down
3) as the magnet passes through the coil there is no change in flux
4) is it leaves, emf is induced and the current opposes the motion therefore it attracts the magnet and so it is slowed again

Question 28

why must lenzs law slow the magnet down

Answer 28

as it is a consequence of the conservation of energy. of the magnet sped up then energy would have Been created.

Question 29

split ring usage

Answer 29

swaps the positive and negative connections every half turn. direction of the current therefore swaps every half turn causing the forces on the coil to always act in the same direction. the coil can continuously rotate in the same direction thanks to this.