7. Magnetism and Electromagnetism

Created by

Lewis Gilbert

Cards (32)

White light is the combination of all the wavelengths in the visible light spectrum
A colour filter absorbs some wavelengths only and transmits certain wavelengths
An object that is see-through or partially see-through can transmit light
Opaque objects absorb are reflect light
An object that absorbs all the radiation it is exposed to is called perfect black body, no radiation is reflected or transmitted through it.
Infra-red RP
Place the Leslie cube on a heatproof mat
Once the kettle has boiled, filled the Leslie cube with hot water.
Ensuring that the thermometer is an equal distance from each of the surfaces on the cube, measure the amount of infrared radiation emitted.
In a convex lens, the light rays enter the lens parallel to one another and then converge at the principal focus after the lens
In a concave lens, the light rays enter the lens parallel to one another and then diverge. The principal focus is the virtual source of the diverging rays before the lens.
A magnifying glass used a convex lens.
Iron, cobalt and nickel are magnetic materials.
A permanent magnet is one with its own magnetic field, cannot be turned on or off.
An induced magnet is a material which becomes and magnet when placed in a magnetic field.
The direction of magnetism is always from north to south.
The core of the earth is made from iron
A compass contains a small bar magnet shaped as a needle, which points in the direction of the earths magnetic field
When a current is passed through a conductor, a magnetic field is induced.
Electromagnets can be turned on or off
The strength of the magnetic field can be increases by increasing the current through the wire
To increase the strength of the magnetic field around a solenoid you can
add an iron core
increase the number of coils in a wire
increase the current passing through the wire
Electromagnetic induction is when a potential difference in created across a conductor due to a change in the magnetic field
Induced potential can be produced by:
moving a magnet in a coil of wire
moving an electrical conductor through magnetic field lines
moving a coil of wire in and out of a magnetic field
Two halves of the split ring commutator ensure that the current is supplied to the wire changes direction each half-turn and as a result, the force produced maintains a constant rotation in one direction
To increase the voltage of an induce potential you can
increase the strength of the magnet
increase the number of turns in the conducting coil of wire
increase the area of the coil
increase the speed of the movement
Turning the magnet more quickly will not only increase the voltage, but also increase the frequency
Microphones
The sound wave vibration in the air particles are transferred to the flexible diaphragm
This causes the diaphragm to move vibrating the coil
The coil moved through the magnetic field of the permanent magnet and induced potential is created
The induced potential causes a current to flow in the closed circuit which the coil is attached to
Headphones
An alternating current us supplied through a coil in the speaker
The produces an electromagnetic field around the wire
The electromagnetic field interacts with the magnetic field of the surrounding permanent magnet and a force is produced
The force produced pushes the cone outwards
A transformer is two coils of wire, the primary and secondary that are connected by an iron core
Step up - increases voltage. the are fewer primary coils than secondary
Step-down - decrease the voltage. There are more primary coils than secondary
Transformers only work for an alternating current and alternating potential difference
An alternating current in a primary oil induces a changing magnetic field in the iron core
The change in magnetic field induces an alternating potential difference in the secondary coil
If the secondary coil is connected to a device then the induced p.d. causes and alternating current
Transformers are almost 100% efficient