Motor Effect: A current-carrying conductor has a magnetic field around it. This field interacts with the magnet's magnetic field and produces a force according to Fleming's Left Hand Rule.
- So the wire experiences a force inside the page.
- Using Newton's Third Law, the magnet experiences a force outside the plane of the page.
F = B x I x L Sin theta
F = B x (Q/t) x L Sin theta
F = B x Q x v Sin theta (when the charge is moving without any conductor)
F = B x e x v Sin theta
e = elementary charge = 1.6 x 10^(-19) C
Q = charge of protons or electrons
B = Magnetic Flux Density
I = Conventional Current
L = Length of conductor inside the magnetic field.
FB is uniform. (B is inside the page)
FB is perpendicular to velocity
FB = FCP
B e v sin theta = m v^2 / r
B e sin theta = m v / r
Q. State and explain the direction of the force on the magnets.
Using Fleming's left hand rule, the force on wire is upwards. Using Newton's third law, the magnet experiences a force downwards.
Note: An electron gains kinetic energy or velocity because of potential difference.
Field of force is a region where a particle experiences a force.
Magnetic field is a region where there is a force experienced by a current carrying conductor.
Fe = FB
E q = B q v
E = B v
v = E / B
I = nave, where n = number density, a = cross-sectional area, v = drift velocity, e = electrons.
VH = (B x I) / (n x t x e) = Hall Voltage
Magnetic field strength is inversely proportional to the square separation, which is known as the Inverse Square Law.
- If mass of charge rises or charge rises, then velocity decreases.
- But if velocity rises, then PB = qv rises. The q will deviate the direction of FB.
Note: A Hall probe uses a semiconductor instead of metal as semiconductor has smaller value of n, hence larger VH.
Q. Explain why a Hall probe is made from a thin slice of material.
Hall voltage depends on thickness of slice. The thinner the slice, larger Hall voltage. Hall voltage is inversely proportional to thickness of slice.
Q. Explain why in order for consistent measurements of magnetic flux density to be made, the current in the probe must be constant.
Hall voltage depends on current in slice.
Q. Briefly describe 4 phenomena associated with the photoelectric effect that cannot be explained using a wave theory of light.
1. Maximum energy of electron depends on frequency.
2. Frequency below which electrons not ejected.
3. Maximum energy of electrons does not depend on intensity.
4. Instantaneous emission of electrons.
Q. Explain the use of a uniform magnetic field and uniform electric field for the selection of the velocity of charged particles.
Electric field is perpendicular to the magnetic field. The velocity of the charged particle is perpendicular to both electric and magnetic fields. Both these forces are equal and cancel out for particles moving at a specific velocity. Given by: V = E/B
Magnetic Flux
SI unit: Weber (Wb)
It is the measure of the total magnetic field passing through a given surface.
= B x A cos theta
B = magnetic flux density (Number of field lines passing through unit area)
A = Area of the surface of the coil
theta = Angle between the normal to Area vector and magnetic field. (Angle between magnetic field and the normal perpendicular to the surface.)
Faraday's Law: In a closed circuit, magnitude of induced emf is directly proportional to the rate of change of magnetic flux linkage through the circuit.
Lenz's Law: Direction of induced electromagnet force in a conductor such that it opposes the change in magnetic flux that produced it.
Faraday's law of electromagnetic induction is the magnitude of induced emf directly proportional to the rate of change of magnetic flux linkage through the circuit.
Q. Use Faraday's law and Lenz's law to explain why the aluminium ring jumps upwards when the switch is closed.
Current in coi produces flux. By Faraday's law, changing flux induces electromotive force in ring. Current in ring causes field. By Lenz's law, field around ring opposes field around coil.
Q. Use the principles of electromagnetic induction to explain why small fluctuations in the current in the spring are found to occur.
The oscillating coils cut magnetic flux as the separation between coils change. Cutting flux causes induced emf. Changing induced emf causes change in current.
Q. With reference to magnetic fields, explain why a force is needed to remove the smaller solenoid.
There is a change in the magnetic flux linkage, which induces emf in the smaller solenoid. So induced current in the smaller solenoid has its own magnetic field. The two magnetic fields interact and have an attractive force.
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