P4 - Electric circuits

P4 - Electric circuits...

• Electric current  is a flow of charge carried by electrons. 
• Electron charge: Proton (think positive)
• The size of electric current is rate of charge flow 
• Current (A) = Charge (C) / Time (s)
• A = amps
• C = coulombs

• In a single closed loop circuit, the current is the same at every point. 
• A diode allows current to flow in one direction only. 
• (1 amp = 1 coulomb per second)

• Potential Difference = Voltage, energy used by a component in a circuit 

• Voltage (V) = work done (J) / Charge (Q)

• Resistance (ohms) = Potential differnce (V) / Current (I)

• Ohms law: 
• Current through a resistor is directly proportional to potentiall difference across the resistor. 

• Reversing the potentiall difference reverses the current through the resistor.

• Potential Difference = Voltage, energy used by a component in a circuit 

• Voltage (V) = work done (J) / Charge (Q)

• Resistance (ohms) = Potential differnce (V) / Current (I)

• Ohms law: 
• Current through a resistor is directly proportional to potentiall difference across the resistor. 

• Reversing the potentiall difference reverses the current through the resistor.

Filament bulb: 

• resistance increases if temperature increses - more particles vibrating, harder for current to flow!

Diode: 

• One direction only. The reverse direction has a very high resistance so there is no current!

Thermistor: 

• resistance decreases as temperature increase 

LDR:

• Resistance decreases as light intensity increases as the light falling on it gets brighter. 

• Components are connected one after the other. 
• If one breaks they all break
• The potentiall difference is shared between all the components. 

• If you add the resistnace of all the components you get the total resistance. 
• The second bulb in the circuit will be dimmer 

• For cells in the same direction, the total potentiall difference is the sum of their induvidual potentiall diffrences. 

• If you add more resistors the total resisitance is increased, as there is less churrent flow.

• Each component is connected along the supply, so if there is a break current can still flow to other branches. 
• Each component is connected across the suppply so the p.d is the same. 
• The total current is the sum of current sthrough the seprate branches. 
• Adding more resistors decreases the total resistance as the total current through the resisttors  is increased and the total potentiall differnce is unchnaged.