P3 Electromagnetism 0.0 / 5 ? PhysicsElectromagnetismGCSEAQA Created by: ColdAsteroidCreated on: 25-01-16 17:08 If there is no current what else is there none of? Magnetic field 1 of 44 What kind of current should there be if there is a magnetic field around the wire? Direct current (DC) 2 of 44 If we change the direction of the current then what else should change? Direction of the magnetic field (Alternating current - AC) 3 of 44 If we can turn the current on and off what do we call this? An electromagnet. 4 of 44 How do we increase the magnetic field of a wire? Coil the wire, increase current, magnetically soft iron core 5 of 44 Where are electromagnets placed? In cranes (iron/steel), loud speaker, door bell 6 of 44 What are the steps for a loudspeaker to work? Step 1 Current passes through coil. Magnetic field produced. 7 of 44 Step 2 Magnetic field now interacts with the permanent magnet. Attraction/repulsion 8 of 44 Step 3 Produces a resultant force for the cone to move. 9 of 44 Step 4 AC causes direction of force to change. 10 of 44 Step 5 Changing direction of field, force means cone in/out=>sound waves. 11 of 44 What are the steps for a doorbell to work? Switch closed=complete circuit and current flows. 12 of 44 Step 2 Electromagnetic field is produce. 13 of 44 Step 3 Iron contact attracted to magnet, clapper hits bell. 14 of 44 Step 4 Current is broken=>Current stops=> electromagnet=off 15 of 44 Step 6 iron contact no longer attracted. Springs back. 16 of 44 Step 7 Circuit is now complete and the process repeats. 17 of 44 What other devices is this process used for? Circuit breakers/other bells 18 of 44 What direction is the magnetic field? North to south 19 of 44 What will happen to a wire carrying current if you place it in a magnetic field? It will experience a force and will move. 20 of 44 Why does this happen? Two magnetic fields interacting 21 of 44 Therefore, what is this effect called? The motor effect 22 of 44 How do we increase the size of the force? Increase:Strength of magnetic field/Size of current 23 of 44 What do the fingers of Fleming's left hand rule mean? Thumb: Motion, First: Field (N-S), Second: Current (+ to -). 24 of 44 What will happen to the wire if it is parallel to the magnetic field? It will not experience a force and therefore not move. 25 of 44 If there is no SRC, then what should happen at 90o? It will stop rotating due to no moment 26 of 44 How do we solve this problem? Switch direction of current 27 of 44 In commercial uses, what do we use for this? A split-ring commutator. 28 of 44 How does the direction of rotation continue? Momentum carries it on, contacts are swapped every half turn 29 of 44 What pole does the wire act as when it goes towards the field? North 30 of 44 Therefore, what does the wire act as coming away from the pole? South 31 of 44 How do we induce a p.d? Conductor through field, field through conductor 32 of 44 What does AC allow the magnetic field to do? Change direction 33 of 44 Why can a DC battery not induce a p.d? Constant magnetic fields don't work 34 of 44 If there are the same number of coils on each side of the iron core what does that mean? Primary coil p.d = Secondary coil p.d 35 of 44 In a step-up transformer, where should the be the most turns? Secondary coil 36 of 44 In step-down transformer, where should there be the most turns? Primary coil 37 of 44 What is the equation of a transformer? Vp/Vs = Np/Ns 38 of 44 What is the equation to find power? P=IV 39 of 44 If we were to find the power of primary and a secondary coil? VpIp=VsIs 40 of 44 Why must power in transformers be conserved? No more energy goes out than comes in. 41 of 44 Why is power always lost? Heating of iron core 42 of 44 What does a switch-mode tranformer do? Operates at high frequencies (50Hz-200kZ 43 of 44 What are the advantages of switch-mode tranformer? Lighter and smaller than trad. tranformers, Very little power (low load) 44 of 44
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