E.I.N.T.K Flashcards
define electrical field
it is a region where a charge that experiences a force
define magnetic field
The region around a magnet where a force acts on another magnet or on a magnetic material
it is a region around a magnet where another magnet experiences a force
describe an electric field around a point charge
positive point charge: arrows go away from the atom
negative point: arrows go towards the atom
which direction does current flow in, in an electric field
arrows go from north to south, left to right if vertical
describe how to charge a body by static electricity
- start off by having a neutral body
- bring a positively charged rod towards the body (all electrons will move to the side with the rod)
- connect the body to earthing (this will bring in more electrons)
- remove earthing first to be stuck with a negative charge
- remove rod last
the above is to negatively charge a neutral body so do the opposite to positively charge a neutral body
- *in step 2 use a -ve charged rod
- *in step 3 when earthing is connected electrons flow into the earth
describe 3 methods of magnetising
- stroking method - stroke a ferrous unmagnetised material with a north pole of a strong magnet and repeat many times
- electrical method - wind a wire round a ferrous material and run a direct current through it
methods of demagnetisation
- hammering
- hit
- using an alternating current
same currents…
attract
opposite currents…
repel
what is a galvanometer
it is a sensitive ammeter
describe what happens when a magnet passes through a galvanometer
- deflection then reverse deflection
(when a north pole passes through) - deflection is larger
(when a south pole passes through first) - as the magnet moves the coil cuts the magnetic field lines inducing an EMF
ways to increase induced EMF
- move the magnet faster - faster speed
- put more turns on the coil
- use a stronger magnet
describe features of a motor
split ring commutator - turns with the coil. each time the coil reaches a vertical position the commutator swap brushes and flow of current is reversed. this means the direction of force is reversed and the coil keeps spinning in the same direction
what can cause a motor to spin faster
- bring magnets closer
- use a stronger magnet
- more turns in a magnet/coil
- stronger current
state the effect of reversing the connections to the battery in a motor
direction of rotation is reversed
describe how an EMF is induced in an a.c. generator
- as the coil rotates one side cuts up the magnetic field lines inducing an e.m.f causing a current to flow
- when the coil reaches the vertical postion, the side that was cut up is now cut down - induced e.m.f will change direction as well as current
what does an alternating current look like on a graph
- similar to sine graph
- V or I on y axis
- time on x axis
what is the purpose of a variable resistor
it controls the amount of current passing through a component (e.g. heater) changing its resistance
what happens when an ammeter reading decreases
- batteries go flat
2. resistance increases decreasing current
the temperature of a thermistor increases so that its resistance decreases
state the effect of this change on the current - explain your answer
current increases as total resistance of the circuit decreases
suggest an advantage of being able to change the current
it prevents overheating
describe in terms of current the difference between a big and small wire
big wire: more current and power, less resistance
small wire: less current and power, more resistance
what happens when a bigger wire is used instead of a smaller wire
power loss is decreased to about quarter of original power as resistance decreases
state 2 sensor devices
LDR
Thermistor
describe action in a thermistor
- when temperature increases (not if the thermistor) resistance decreases
- when temperature decreases the resistance increases
describe action of a LDR
- when light intensity increases resistance decreases
- when light intensity decreases resistance increases
what happens to resisitance when V or I or P increases
resistance decreases
what is a potential divider
just a circuit with 2 resistors
a circuit has a LDR in series with a resistor and a lamp across the resistor
what change is made in the circuit to make the lamp glow brightly
-increase current flowing through the lamp by increasing the voltage across it through increasing light intensity of the LDR which will reduce the resistance
describe a circuit in series
- current is the same through out
- all components are switched on at the same time
- voltage is shared/divided meaning different brightness in lamps
- if one lamp is faulty whole circuit breaks
describe a circuit in parallel
- current is divided/shared
- voltage is the same through out
- switched on/off individually
in a transformer why is the iron core laminated
to reduce energy loss
how is an emf induced in a transformer
the a.c. emf at the primary coil induces a magnetic field in the iron core. this alternating magnetic field is cut by the secondary coil producing an EMF in the process
formulas in transformers
Np/Ns = Vp/Vs VpIp = VsIs
state 3 methods of charging objects
- rubbing
- induction
- earthing
