Electricity Flashcards
WHAT CHARGES ATTRACT AND REPEL
positive + positive = repel
negative + negative = repel
positive + negative = attract
WHAT IS ELECTRIC CURRENT
The electric charge transferred per unit time.
WHATS A CONDUCTOR AND INSULATOR
Conductor - Something that allows electrons to move freely - metals.
Insulator - Somethinv thag doesn’t allow electrons to move freely - wood
WHAT IS ALTERNATING CURRENT (A.C)
Flow of electrons regularly changes direction.
The voltage varies from 0 to peak voltage in one direction then back to 0 then to peak voltage in the opposite direction e.g mains power
WHAT IS DIRECT CURRENT (D.C)
The electrons flow around the circuit in one direction
The voltage remains constant eg battery power.
WHAT DO CHARGED PARTICLES HAVE AROUND THEM
Electric fields apply a force to them and make them move. The path it follows depends on the electric field.
A charged particle experiences a force in an electric field.
TWO OPPOSITELY CHARGED PLATES
A proton would move towards the negative plate.
- Always use a positive charge to determine field lines.
- Closer field lines = Stronger charge.
- Curved lines at end.
Parallel lines - field is uniform (the same)
POINT CHARGE
(RADIAL FIELD)
Positive charge placed in the field would move away.
TWO OPPOSITELY CHARGED POINTS
If a positive charge was placed on the field lines, it would move towards the negative point.
TWO LIKED CHARGE POINTS
If a positive charge was placed on the field lines, it would move away following the curved lines.
WHAT IS POTENTIAL DIFFERENCE (VOLTAGE)
Potential difference measures how much energy the supply gives to each coulomb of charge.
9V battery means 9 joules to each coulomb.
SERIES CIRCUIT RULES
- Only has one loop and everything would be turned off if there was a break in the circuit or a switch is switched.
- The voltage adds up to the supply and the current is the same throughout all points.
PARALLEL CIRCUIT RULES
- Has multiple branches.
- The currents add up to the supply current and the current increases as more branches are added.
- The voltages are the same at all points.
- A break in the circuit only affects the broken branch.
WHAT IS RESISTANCE
Anything in a circuit resists and the more it resists the higher its resistance.
Opposes current
Resistance in series = RT=R1+R2+R3…
If more resistors are added in series, the current decreases. (resistance increases).
Resistance in parallel = 1/RT=1/R1+1/R2+1/R3…
If more resistors are added in parallel, the current increases (resistance decreases).
WHAT IS OHMS LAW
Ohms law is the relationship between potential difference and current. This leads to the idea of resistance.
WHAT IS THE OHMS LAW EXPERIMENT
How does the potential different across a resistor affect the current in the resistor.
Vary the potential differences across the resistors by turning the control on the power supply. Record the current in the resistors at different potential differences.
Straight line through origin. Voltage is directly proportional to current.
The gradient of a VI graph is the value of resistance.
Ohmic conductors obey ohms law. Straight line and a positive gradient.
Non-ohmic conductors don’t obey ohms law eg bulb. It follows a curved line with an increasing gradient. Resistance increases as the current increases.
WHY DOES RESISTANCE INCREASE WITH TEMPERATURE
Example: filament wire of a bulb.
As the voltage increases, the wire heats up. This makes the atoms in the wire vibrate more which makes it difficult for the electrons to move along the wire - resistance increases.
Old fashioned filament lights always pop when turned on because the current will be higher when put on and is more likely to break as the resistance will be lower.
WHATS A CELL AND SYMBOL
Produces electrical energy
WHAT IS A BATTERY AND SYMBOL
Series of cells, increases energy compared to cell
WHAT IS A LAMP AND SYMBOL
electrical energy to light energy.
WHAT IS A SWITCH AND SYMBOL
When opened, circuit breaks, no current. When closed, makes a circuit, current exists.
WHAT IS A RESISTOR AND SYMBOL
opposes current in a circuit, electrical to heat.
WHAT IS A VOLTMETER AND SYMBOL
measures voltage, connected in parallel
WHAT IS AN AMMETER AND SYMBOL
measures current, connected in series
WHAT IS AN LED AND SYMBOL
arrows always direct NE. If you reverse the connections it will not light as current can only flow in one direction. It is destroyed by high currents. A series resistor needs to be fitted to the LED to reduce current to a safe level. electrical to light.
Maximum voltage - 2V
Maximum current - 20mA
NO HEAT
WHAT IS A MOTOR AND SYMBOL
Electrical to kinetic
WHAT IS A MICROPHONE AND SYMBOL
sound to electrical
WHAT IS A LOUDSPEAKER
electrical to sound
WHAT IS A PHOTOVOLTAIC CELL (SOLAR CELL) AND SYMBOL
light to electrical
WHAT IS A FUSE AND SYMBOL
If an appliance starts to draw too high a current, the thin wire in the fuse melts and cuts off the current. This stops a flex from overheating and a potential fire.
If an appliance has a power raging or less than 720W - 3A fuse. If greater, use 13A.
Using formula PIV, current less than 3A, use 3A. If current between 3A and 13A, use 13A.
Safety device in a plug or electrical component.
WHAT IS A DIODE AND SYMBOL
Only allows current in one direction. Can protect a circuit from a power supply being connected the wrong way. Can also change A.C to D.C
WHAT IS A CAPACITOR AND SYMBOL
Two metal plates seperate by an insulator to store electric charge. The voltage across a fully charge capacitor is equal to the supply voltage. (Voltage takes time to rise to the supply).
Timing device - street lights.
The time for a capacitors chats to be altered is affected by the value of the capacitor - the bigger the capacitance the longer it takes to charge.
- The size of the charging current as the larger the current is, the shorter the time for the capacitor to charge.
The capacitor is ussually altered by using a variable resistor.
WHAT IS A VARIABLE RESISTOR AND SYMBOL
Adjusting the variable resistor allows you to adjust when the circuit switches on and off. Increasing the resistance of it will have the opposite effect and turn the heating on at a higher temperature. (resistance can be changed by temperature).
WHAT IS AN LDR AND SYMBOL
It is a resistor which is dependant on light level. Higher light level means lower resistance - street lights turn on when it’s dark.
As light intensity increases, the resistance decreases.
WHAT IS A RELAY AND SYMBOL
Switch operated by magnetic field. When the first circuit is complete. the current in the coil causes it to become magnetised, pulling shut the switch in the second circuit. Low current circuit can then be used to control a high current circuit.
Pressing the switch on a low current DC circuit will turn on the bell in the high current AC circuit.
WHATS AN NPN TRANSISTOR AND SYMBOL
Used as an electronic switch which is voltage controlled. If high enough voltage is applied to the base of the transistor, then current flows between the collector and emitter. Voltage above 0.7V causes transistor to switch on.
WHAT IS A MOSFET TRANSISTOR
Mosfets switch on at a higher voltage, 2V. They can handle bigger output current than npn transistors, so can run in bulbs and motors.
WHAT IS A THERMISTOR AND SYMBOL
Type of resistor where resistance depends on heat, Higher temperature lower resistance - electrical heaters.
WHAT IS A POTENTIAL DIVIDER
It’s a way of dividing up the voltage from a supply. This means we can get the exact voltage needed to operate a circuit.
A voltage divider circuit is a circuit that divides a voltage into two or more smaller voltages.
In a potential divider circuit, The higher the resistance of a resistor, the higher the voltage across it.
Series circuit = current same at all points.
IF YOU DONT KNOW THE SUPPLY VOLTAGE YOU USE… (POTENTIAL DIVIDER CIRCUITS)
V1/V2 = R1/R2
IF YOU KNOW THE SUPPLY VOLTAGE USE… (POTENTIAL DIVIDER CIRCUITS)
V2 = R2/R1+R2 x VS
WHAT WAY DOES A CIRCUIT MOVE
+ -
WHATS AN INPUT AND OUTPUT DEVICE
Input - Form of energy to electrical.
Output - Electrical to form of energy.
CIRCUIT SYMBOL FOR A.C
Two circles with squiggle in the middle.
SYMBOL FOR D.C
Two circles with + and -.
