Electricty Flashcards
What is the Charge (A)?
- Rate of flow of charge round the circuit
- Electrons carry charge - negatively charged particles
- Current only flow if there’s voltage
What is the Voltage (V)?
- Drives current round circuit
* Also called - potential difference
What is the Resistance (ohm)?
- Anything In circuit that slows the flow down
* More components = higher overall resistance
What happens if you Increase the Voltage?
More current will flow
What happens if you Increase the Resistance?
Less current will flow
What is the Ammeter?
- Measure current flowing through component
* Placed in series anywhere in main circuit, never in parallel
What is the Voltmeter?
- Measure voltage across component
* Placed in parallel around component, not around variable resistor or battery
What happens when you Vary the Variable Resistor?
Alters current flowing through circuit
What is the Mains Supply?
- A.C
* Current constantly changing direction
What is the Battery Supply?
- D.C
* Current constantly flowing in same direction
Voltage =
Current x Resistance
How does current in a Wire vary as you change the voltage?
Current through wire is proportional to voltage
How does current in Different Resistors vary as you change the voltage?
- Current through resistor is proportional to voltage
* Different resistors have different resistances (different slopes)
How does current in a Metal Filament Lamp vary as you change the voltage?
As temperature of metal filament increases, resistance increases, curve graph
How does current in a Diode vary as you change the voltage?
Current flow through diode in one direction
What are Light Emitting Diodes and give an example?
- Emit light when current flows through them in forward direction
- Used for numbers on digital clocks, traffic lights, remote controls
What is a Light Dependent Resistor?
- Changes resistance depending on how much light falls on it
- Bright - Resistance falls
- Dark - Resistance highest
What is a Thermistor?
- Temp dependant resistor
- Hot - Resistance drops
- Cold - Resistance increases
What are Series Circuit?
- Components connected in line, end to end, between +ve & -ve of power supply
- Remove 1 component, circuit broken, stop working
What is in a Series Circuit?
- Bigger supply p.d when more cells are in series
- Current same everywhere
- Potential difference shared between components
- Resistance depends on number of components and type of component used
What are Parallel Circuits?
- Component separately connected to +ve & -ve of supply
* Remove 1 component, won’t affect others
What is in a Parallel Circuit?
- Potential difference same
- Current shared between branches, total current flowing around circuit = total of all currents
- Current through branch depends on resistance of brach - higher = harder for charge to flow, lower current
- Total Resistance decreases when add 2nd resistor in parallel
What is Voltage?
Energy transferred per unit charge passed
What is Current?
Rate of flow of electrical charge around a circuit
Power=
Current x Time
What happens when a Charge drops through a Voltage?
- Energy is transferred
* Bigger change in Voltage = the more energy transferred
What is the Equation linking Energy Transferred, Charge and Voltage?
Energy transferred = charge x voltage
What is the Equation linking Energy Transferred, Charge, Current and Resistance?
Energy transferred = charge x current x resistance
What are the Wires in a plug and what are the Colours of them?
- Live - Brown
- Neutral - Blue
- Earth - Green/Yellow
What is the Voltage of the Neutral Wire?
0
Where does Electricity Flow?
Flows in through the live wire and out through the neutral wire
If an appliance has a Metal Case what needs to happen so it will be Safe?
- Earthed to reduce danger of electric shock
* Earthed conductor never becomes live
What are the Earth Wire and Fuse for?
Safety and work together
How does Earthing and Fuses prevent Fires and Shocks?
- If live touches metal case, big current flows through live & case & out down earth wire
- Surge in current melts fuse in live wire
- Isolates appliance, impossible to get electric shock, prevent fire caused by heating effect of large current
What are Circuit Breakers?
- Electrical safety device used in circuits
* Protect circuit from damage if too much current flows
How are Circuit Breakers more Convenient than Fuses?
- They detect surge in current, break circuit by opening switch
- Circuit breaker easily reset by flicking a switch on device
- So more convenient, fuses replaced once melted
What is a Residual Current Circuit Breaker (RCCB)?
- Detects difference in current, cuts off power by opening switch
- Operate faster than fuses
- Work for small current changes that fuses can’t melt
Electrical Power =
Current x Voltage
What is Electrical Power?
- Rate at which an appliance transfers energy
* Appliance with high power rating transfer a lot of energy quickly, will draw large current from supply
What does Energy Transferred by appliance Depend on?
Power of appliance and how long it is on for
What to Like and Opposite Charges do?
- Opposite - attract
- Like - Repel
- Forces weaker further apart
What do Conductors do and give an example?
- Conduct charge easily
- Current can flow through them
- Metals (copper, silver, etc)
What is a Static Charge?
Charge builds up in one place and not free to move
What is a Cause of Static Electricity?
- Friction
- 2 insulating materials rubbed together, electrons transferred from one to another
- -ve electrostatic charge on one,+ve on other
How can Cars get a Static Charge?
Gained or lost electrons from air rushing past them as travel at high speeds
What happens as Electric Charge builds up on an isolated object?
- Voltage between object & earth increases
- Voltage large enough - electrons jump between charged object & earth - this is a spark
- Also jump to earthed conductors
What’s an Example of Static Electricity being Helpful using a Photocopier?
- Image plate +ve charged
- Image of what your copying projected onto it
- White bits make light fall on plate, charge leaks away in those places
- Charged bits attract -ve charged black powder, transferred onto +ve paper
- Paper heated so powder sticks
- Photocopy now made
What’s an Example of Static Electricity being a Problem using Lightning?
- Rain & ice bump together in storm clouds
- Knock off electrons, top of cloud +ve charged, bottom -ve charged
- Creating huge voltage & big spark
How do you Test whether a Rod of material is Charged?
- Suspend rod with known charge on thread , see if there repulsion or attraction when rod close
- Attraction - Test rod has opposite charge to suspended rod
- Repulsion - Test rod has same charge to suspended rod
