hey,
i found this in the resources section. Notes by Acmilan
A galvanometer is an instrument that measures small electric currents. In a galvanometer there is a current carrying coil inside a radial magnetic field. When the current that has to measured flows through the coil, it will experience a force in the magnetic field (motor effect). A coiled spring is attached to the current carrying coil, which tightens as the spring rotates until the restoring torque of the spring balances out with the force on the coil. The coil will move further as the current supplied is larger before the two torques balance out and stops the coils movement. The torque of the coil is given by τ = nBAIcosθ and the torque of the spring is given by τ = kφ (where k is a constant and φ is the angle at which the spring is turned). When the two torques balance out, nBAIcosθ = kφ. Since n, B, A, θ and k are all predetermined, the angle at which the coil rotates (φ) is proportional to the current (I),hence measuring the current by the angle turned. This is indicated on a scale in the galvanometer through a pointer connected to the rotating coil.
- the loudspeaker
In Loudspeakers, electrical signals are converted into sound. These signals are sent to a coil attached to the cone of the speaker. A permanent magnets surround the coil so that a magnetic field exists from the cone outwards. Since current carrying conductors experience a force in a magnetic field (motor effect), the force will be forwards or rearwards according to the direction of the current. The coil is attached to a paper diaphragm. The changing electrical current will cause the cone and hence the diaphragm to vibrate back and forth because they experience a force. This causes the air to be pushed back and forth producing sound that travels to the person’s ear. Turning up the volume will be a result of an increase in electric current, causing the cone to vibrate with greater force and produce higher amplitude.
hopefully it helps
PS. Plz search the resources section be4 asking next time.
