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Physics Mag Fields
Physics Spring Y13
| Question | Answer |
|---|---|
| Arrow direction | The way a free north pole would move. From N to S. Earth direction opposite. |
| Uniform field | Equally spaced and parallel magnetic field lines |
| bar megnet | Strongest (lines closest together) at poles |
| Electromagnetism | When a wire carrying a current, a magnetic field is created around the wire. Any charged particle that moves creates a magnetic field in the space around it. ALWAYS use conventional current |
| Solenoid field shape | Bar magnet but line go through middle. |
| RH grip rule | Thumb in direction of CONVENTIONAL current, fingers show wire curling. |
| Wire current symbols | Dot out of page. X into page |
| What is B? | Magnetic flux density |
| Current carrying wire in magnetic field | Where lines in same direction, add (more dense). Other side subtract (gap). Force in direction of the gap because of difference in magnetic field. Called a catapult field. Motor effect |
| Motor effect | Fleming's Left Hand Rule. FBI (force thumb, then magnetic field, then CONVENTIONAL current) Depends on angle between magnetic field and current (sin theta), length of wire *in magnetic field*, current, magnetic flux density (field strength) |
| SI unit for B | Tesla (T) Nm^-1A^-1 |
| When calculating gradient | ALWAYS state it to get working marks |
| Beam of electrons through mag field | Can be seen as a (reversed) current flow Electrons travel in a circular path in the region of the uniform perpendicular magnetic field, and the force on the electrons is always at right angles to motion |
| Wire N3L | Remember wire forms N3L pair on magnet too |
| Force on charges in wire | Electrons in of wire in L length of mag field. Force on every charge = BIl l = vt F = BIvt I = Q/t If N charges in length L, then I = NQ/t (current needs to use N) F = BNQv so on each F = BQv |
| Linking force of charges in wire | Centripetal force = F = mv^2/r F = BQv = mv^2/r r = mv/BQ = momentum/BQ |
| Velocity selector | Electric field pointing downwards. Mag field into page (so acting upwards). Electrons fired in to slit on far end. |
| Velocity selector purpose | Magnitude of force due to electric constant due to charge. Mag of magnetic field dependent on v Only particles of certain v will balance and go through slit. This is when qE = Bqv v = E/B |
| Velocity selector after slit | Mag field extends past. We know v (and we're looking for m) so can calc radius of turn for placing the electron detector after their circular path in mag field without electric. |
| Charges in mag field | Can only be affected if moving. |
| Velocity selector for mass spectrometer | Radius of curve dependent on mass as they all have the same velocity. |
| Shape of electric vs magnetic field electron flo | E force always same direction so parabola, in B force is always at right angles so circular. |
| Magnetic Flux unit | Webers (Wb) |
| Magnetic Flux | The magnetic flux density multiplied by the area perpendicular to the field direction. phi = BAcostheta where theta is the angle between the area used and the area perpendicular |
| Field lines aka | Lines of flux |
| Magnetic flux linkage (not mock) | In electromagnetism, coils of wire are often used. Magnetic flux linkage = N x phi where N is the number of turns on the coil |
| Generator effect (not mock) | Fleming's Right Hand Rule. Fingers the same. Kinetic to electric unlike opposite for motor |
| Faraday's Law (not mock) | States that induced emf is equal to the rate of change of magnetic flux linkage. Emf = -N*phi/delta(t) where N*phi is the magnetic flux linkage. Minus sign is there to satisfy Lenz law |
| Check photos Taylor whatsapp 22:44 09/01/2026 |
Created by:
Pyrogearos2