Electricity Flashcards
What is needed for electrical charge to flow through a closed curcuit?
A source of potential difference
What is electric current?
A flow of electrical charge
What is the size of electric current?
The rate of flow of electrical charge
What is charge flow measured in?
Coulombs
What is current measured in?
Amperes
What does the current through a component depend on?
The resistance and potential difference of the component
How are resistance and current linked?
The greater the resistance of the component, the smaller the current for a given potential difference
What is potential difference measured in?
Volts
What is resistance measured in?
Ohms
What happens when the temperature of a filament increases?
- resistance increases
What happens when the temperature of a thermistor increases?
- resistance decreases
What are some applications of thermistors?
- thermostats
- car engine temperature sendors
What happens when light intensity on an LDR increases?
- resistance decreases
What are the applications of LDR’s?
- automatic night lights
- outdoor lighting
- burgular lighting
What are components connected in series like?
- same current through each component
- total potential difference of power supply shared between the components
- total resistance of two components is the sum of resistance of each component
what is the equation for total resistance?
resistance 1 + resistance 2 (ohms)
What is the mains current in UK?
230V
What is the mains frequency UK?
- 50Hz
Describe the live wire.
- Brown
- carries alternating potential difference from the supply
Describe the neutral wire.
- Blue
- at or close to, earth potential (0V)
- completes the curcuit
Describe the earth wire.
- Green and yellow stripes
- 0V, only carries current if there’s a fault
What is power measured in?
Whatts
Why is the live wire dangerous?
- causes large electrical shock that could injure or even kill you
- could result in fires in contact with earth wire
What is the national grid?
- system of cables and transformers linking power stations to consumers
What do step up tranformers do?
- increase PD from power station to transmission cables
- decrease current
- to reduce energy loss
What do step down transformers do?
- decrease potention difference
- increase current
- for domestic use
Describe static electricity.
- insulating materials rubbed against each other and become electrically charged
- negatively charged electrons rubbed off one material and on to other
- material that gains electrons become negatively charged
- material that loses electrons becomes positively charged
Describe what happens when two electrically charged objects are brought together.
- exert a force on each other
- repel if carry same charge
- attract if carry opposite charges
- attraction and repulsion non contact forces
Describe electric fields.
- charged object creates electric field around itself
- field strongest close to charged object
- further away from the charged object, weaker field
how do the earth wire and fuse protect user from electric shock?
• fault develops when live wire touch metal casing
• resistance in live wire reduces
• current in live wire increases
• earth wire takes current from live wire
• at the same time fuse melts
• so no more current flows into live wire
how do the earth wire and fuse protect user from electric shock?
• fault develops when live wire touch metal casing
• resistance in live wire reduces
• current in live wire increases
• earth wire takes current from live wire
• at the same time fuse melts
• so no more current flows into live wire
