2. Current There are two types of current…… Direct current (dc) in which the current travels in one direction only Alternating current (ac) in which the current alternates (changes direction) 50 times a second

3. Transformers – How they work Primary coil An alternating current in the primary coil Induces a magnetic field through the core which… Induces an ac current in the secondary coil Secondary coil Iron core

4. Transformers – changing voltage & current More turns on the secondary coil means it is a step up transformer VOLTAGE UP, CURRENT DOWN 50 turns 100 turns More turns on the Primary coil means it is a step down transformer VOLTAGE DOWN, CURRENT UP 50 turns100 turns Primary side Secondary side

5. 50 turns Same number of turns on each side Means…….. It is an isolating transformer. Example would be a shaver. If water gets on the mains side it stops you getting a shock as the wires aren't touching The live parts will not touch the Earth so a large current cant flow through you

6. Calculations – easy if you follow the steps T p 50 =turns Primary side V p = 12V Secondary side V s = ? T s 150 =turns You are always given three of the four variables 1.Voltages one side, number of turns on the other Vs Ts Vp Tp 2. Put in the numbersV s 150 12 50 = = 150 x 12 = 36V 50

7. This time you need to find V P T p 50 =turns Primary side V p = ? Secondary side V s = 12 T s 150 =turns You are always given three of the four variables 1.This time you put the primary side on the topVp Tp Vs Ts 2. Put in the numbersV p 50 12 150 = = 50 x 12 = 4V 150

8. Transformers and the National Grid The Grid transmits electricity throughout the country at a high voltage This is because it results in a low current which reduces the energy loss as heat The power loss as heat can be found using the formula P = I 2 R Where R = resistance in ohms

9. Diodes & Capacitors A diode changes alternating current into direct current ? A.C turns into ……… This is called half wave rectification This wastes half the current

10. Four diodes connected the correct way result in full wave rectification

11. Charging a capacitor + + - - Charge can be stored on a capacitor The capacitor has a voltage across it M When connected the capacitor discharges The current will be large at first but drop quickly Because the voltage across the capacitor drops

12. Capacitors and diodes in a circuit together What do they do?????????? Smooooooooooth out the current