P6 - Electricity for Gadgets

  switch      buzzer     motor  ammeter

rheostat- variable resistor, made from coils of wire, you can change resistance

• a thiliment bulb does not obey Ohm's law

potential dividers - used to produce a required voltage in a circuit 

2 fixed resistors can be used as a potential divider

thermistor - resistor dependent on temperature , if temperature if high, resistance if low, a negative temperature is efficent

LDR- resistor dependent on light intensity  

transistors - an electrical switch, it can be turned on or off. An average computer has millions of transistors  

• When the base & emitter voltage = 0 or low, no current flows in base-emitter
• This means no current can flow between collector & emitter
• When voltage of base & emitter = high a small current flows through base-emitter 
• this allows large current in collector & emitter
• a small current in base emitter acts like a switch that 'turns on' the large current in collector
• emitter current = base collector + collector current

• use semi-conductors that are particularly arranged to allow current to pass one way 
• light is emitted when a current flows through the semi conductors
• an NPN transistor can be used as a switch for LEDs when connected with 3 reistors 
• a resistor is connected in parllel to limit current, preventing damage
• no current in base cuaes transistor to switch off so the LED switchs off
• when small current is in base it causes transmitter to turn on, so large current can flow into collector emitter, so LED lights up

AND gate       OR gate    NOT gate

 Nand gate   Nor gate

• a relay switchs mains current, so the low power logic gate would not be directly exposed to mains power preventing damage. The relay isolates the low voltage in the sensing circuit from the high voltage.

all generators generate AC current

factor effecting:

• if you double the turns, you double the voltage
• double speed and the voltage doubles, if you increase the speed, you increase the number of rotations per second therefore increasing the frequency

mains frequency = 50Hz

• electrons move into the positive space & flow making a current 
• this doesn't happen if current is in a negative direction or if current is positive it causes the electrons in layer N to move to layer P

diode           capacitor      diode resistance graph

• negative current is blocked by high resistance diode
• positive current easily passes through