2-Electricity Flashcards
What is current
The flow of electric charge
I
What is the unit of current
Ampere
A
What is potential difference
The driving force that pushes charge around
V
What is the unit for potential difference
Volt
V
What is resistance
Slows the flow down
R
What is the unit of resistance
Ohms
Omega symbol
What does greater resistance do to the current
The greater the resistance, the smaller the current
What is the equation for charge flow
Charge flow (C) = Current (A) x Time (s)
Q=It
What is the equation linking potential difference, current and resistance
Potential difference (V) = Current (A) x Resistance (ohms)
V=IR
What is the ammeter used to measure
The current in amps
How do u use an ammeter
Must always be placed in series with whatever is being investigated
What does the voltmeter measure
Potential difference in volts
How is the voltmeter used
Must always be placed in parallel around whatever is being investigated
How r resistance and length of wire linked
They r directly proportional
What systematic error can be made whilst doing the length of wire practical
The first clip might not be attached exactly at 0cm so all lengths may be slightly out
What should I-V graph for an ohmic conductor look like
A straight line as they are directly proportional
What should the I-V graph for a filament lamp look like
Starts out as a straight line and then curves into a plateau
Why does the I-V graph for filament lamp curve
Because as the current increases, the temperature increases so the resistance increases. The current then decreases
What does the I-V graph for a diode look like
Steep line on the right side that goes into the x axis and stays along there
Why does the diode I-V look as it does
Because the current only flows in one direction so has a very high resistance in the reverse direction
What does LDR stand for
Light dependent resistor
When does an LDR have the most resistance
In darkness
When is an LDR have the least resistance
In bright light
What can LDRs be used for
Automatic night lights, burglar detectors and outdoor lighting
What is a thermistor
A temperature dependent resistor
When does a thermistor have the most resistance
Cold conditions
When does a thermistor have the least resistance
Hot conditions
What can thermistors be used for
Car engine temperature sensors and electronic thermostats
What is a sensing circuit
Can be used to turn on or increase the power to components depending on the conditions that they r in
What happens in a series circuit if u remove or disconnect one component
The circuit is broken and they all stop
How is potential difference distributed through a series circuit
The total pd of the supply is shared between the components
How do u calculate the total pd round a series circuit
Add up all the voltages
V(total) = V(1) + V(1) + …
How is current distributed throughout a series circuit
The same current flows through all the components
How his total resistance calculated in a series circuit
The sum of all the resistance
How is pd distributed throughout a parallel circuit
The pd is the same across all the components
How is current distributed in a parallel circuit
The current is shared between each branch
What does adding another resistor in parallel mean
The total resistance decreases
Why does the total resistance decrease when another resistor is added in parallel
Because there r more areas for the current to go so the current increases.
An increase in current means a decrease in resistance
What does ac stand for
Alternating current
What does dc stand for
Direct current
How is the current flowing in ac supplies
Constantly changing direction
How is the current flowing in dc supplies
All flowing in the same direction
What is the voltage type in ac supplies
Alternating voltage
What is the voltage type in dc supplies
Direct voltage
What is frequency or cycles per second’s unit
Hertz
Hz
What colour is the neutral wire
Blue
What is the colour of the live wire
Brown
What is the colour of the earth wire
Green and yellow
What is the function of the neutral wire
It completes the circuit. When the appliance is working the current flows through live and neutral wires
What is the pd of the neutral wire
0V
What is the function of the live wire
Provides the alternating pd
What pd is the live wire
230V
What is the function of the earth wire
Stops appliance casing from becoming live.
If there is a fault it sends the current to the ground
What is the pd of the earth wire
0V
Why can the live wire cause an electric shock
Your body provides a link between the wire and the earth and the current flows through you.
There is a large pd across your body because the earth is 0V and the wire is 230V
What is the equation for energy transferred linking to power
Energy transferred (J) = Power (W) x Time (s)
E=Pt
What is the equation for energy transferred linking to charge flow
Energy transferred (J) = Charge flow (C) x Potential difference (V)
E=QV
What is the equation for power linking current and pd
Power (W) = Potential difference (V) x Current (A)
P=VI
What is the equation for power linking current and resistance
Power (W) = Current*2 (A) x Resistance (ohms)
P=I*2R
What is the national grid made up of
A giant system of cables and transformers that connects power stations and consumers
Why is having really high voltage better than current
Because having high current means that the wire heats up and lots of energy is lost to the surroundings
What pd are the wires for transporting energy on the national grid
400,000V
If the transformers are nearly 100% efficient then how could the power of them be written
Power in primary coil = power in secondary coil
What materials are rubbed together to build up static
Certain insulating materials
What does rubbing the two insulators do to electrons
The electrons are scraped off one and dumped on the other
What r typical examples of materials used for static
Polythene rod or acetate rod with a cloth duster
Why can sparks occur
When the electric charge from static builds up too much and the pd gets large enough the electrons can jump across the gap between the charged object and the earth or any earthed conductors (could be people)
What is it called when objects move due to having the same or different charges
Electrostatic attraction / repulsion
How can u show electric fields
Field lines
If the object is positively charged then what direction r the arrows going in the field lines
Away from the object
If the object is negatively charged what direction r the arrows going on the field lines
Towards the object
What happens to a charged object when placed in an electric field
It feels a force, either attraction or repulsion
What does a strong electric field do to air
The electrons in the particles are removed.
Ionised
What happens to air when it is ionised
It becomes much more conductive so the current flows through it if there is a higher enough pd and this is spark
