Electricity - Y10 Flashcards
Electric current,what direction, conventional current
Rate of Flow of electrons - positive (long) to negative (short)
P.d and Current in series
P.d = Shared
Current = Same
P.d and Current in parallel
P.d = Same
Current = Shared
Name every single formula
- Q = I t
- E = Q V
- V = IR
- E = P T
- P = V I
- P = I²R
What is p.d?
Difference of electric pressure between 2 points/ driving force that pushes the current
What is the correlation between current and voltage?
Directly proportional when the resistance is constant (and temp.). An ohmic conductor follows this graph.
What happens if you increase resistors in series?
Total Resistance increases
What happens if you increase resistors in parallel?
Total resistance decreases
What is Ohms law?
Current is directly proportional to voltage when the temp. is constant
Name 4 non ohmic conductors
- Filament lamp
- Diode
- LDR
- Thermistor
Function of diode
Current only flows in 1 direction
LDR Resistance
Dark light = high resistance, little current
Bright light = low resistance, high current
Thermistor resistance
Low temp = high resistance, little current
High temp = low resistance, high current
Resistance decreases as temp increases
Whats AC?
Alternating current is constantly changing
What is DC?
Direct current is either positive/negative and in the same direction
What is DC used in?
Cells/ batteries
Is mains supply AC or DC?
AC
Voltage and frequency for mains supply?
230V and 50 Hz
Which has a higher p.d, AC or DC?
AC
Is the p.d negative or positive in AC?
Both
Why are the 3 pins inside a plug made out of brass?
Good conductor, doesn’t rust. It’s an alloy so it’s harder than a metal
What colour is the live wire?
brown
What colour is the earth wire?
green and yellow
What colour is the neutral wire?
blue
What happens to the total current and resistance in the circuit when one resistor is removed? (PARALLEL)
- Total current would decrease
- As there are more paths for the current to pass through
Whats the function of the earth wire?
Protects the wiring and for safety - stops appliance casing becoming live
earth wire pd
0V
Function of live wire
Provides the alternating pd
live wire pd
230V
Function of neutral wire
Completes the circuit - when appliance is operating, current flows through live and neutral wires
pd of neutral wire
0V
How does the live wire give an electric shock?
The body is 0V, live wire has a 230V which produces an electric shock that could injure/kill you
What does a step-up transformer do?
Increases voltage, reduces corrent which reduces the energy loss by heating wires
What does a step-down transformer do?
Reduce voltage to 230V, increase current
What is static electricity?
When neutral atoms become charged due to friction, Frictional forces result in a transfer of electrons, this causes atoms to become charged ions
Can metals be statically charged, why?
No because its a conductor so electrons just flow straight back again
Explain static electricity between a jumper, balloon and wall
- Balloon and jumper have both negative and positive particles, they are both neutrally charged with the same number of electrons
- Friction causes the electrons to transfer. The shirt has lost electrons and the balloon gains electrons
- Like charges on the wall repel and opposite charges on the wall attract, which makes the balloon stick on the wall - creates induced charge on wall
What is an electric field?
Area where charges will experience a force/ show how it will react
What is the direction do the arrows on a positively charged metal sphere?
Outwards
What is the direction do the arrows on a negatively charged metal sphere?
Inwards
Where is the electric field the strongest?
When it’s close to the charged object because field lines are closer.
How are the field lines placed?
Perpendicular/right angle
How are sparks formed?
- When there is a high enough pd between a charged object and the earth/ earthed object
- High pd causes a strong electric field between charged and earthed object
- Strong field causes electrons in air articles to be removed (ionisation)
- Air is normally an insulator but when its ionised its more conductive so a current can flow through, creating a spark
What is the power rating on an appliance?
Maximum operating power
How can you investigate how the length of a wire affects the resistance
- Attach croc clip to wire at 0cm
- Attach 2nd croc clip 10cm away, write it down on a table
- Close switch and recond current and pd
- Open switch and place croc clip 10cm away
- Record new length, current, pd
- Repeat
- Caculate resistance for each length of wire
- Plot graph - resistance and length of wire - graph should be straight line, longer the wire, greater the resistance
Describe an experiment how adding resistors in series affects total resistance
- Have 4 identical resistors
- Create circuit with resistor,ammeter and battery
- Measure current, using current to find out resistance
- Add anotherr resistor in series
- Measure overall resistance with current and pd of battery
- Repeat until you use all 4 resistors
- Plot a graph - number of resistors and resistance
Describe an experiment how adding resistors in parallel affects total resistance
- Use 4 identical resistors
- Place 2 resistors in parallel with ammeter and battery
- Find the resistance using pd and current
- Repeat
- Plot a graph
What is charge?
A measure of the total current that flowed within a certain period of time
role of oscilloscope
display how voltage changes with time
Why shouldnt you touch a socket even when its off?
Live wire still has a high pd - could cause a shock
What are surges?
Sudden in increases in current , happens when you turn an appliance on or off or a fault in the circuit or appliance
fires, electric shocks caused
What happens to fuses and circuit breakers when the current gets too high
- Fuse has a very thin wire between the live wire
- If there is a surge, huge amount of current will flow throught live wire and flow through the fuse
- wire heats up and melts, breaks current, no current can flow.
Pros and cons of fuses
- simple and cheap
- permanently broken after a single surge - need to be replaced each time
what are ciruit breakers?
- similar to fuses
- dont get permanently damaged, they get tripped (turn off the current)
- can easily reset
- expensive
What is double insulation?
- Covered in plastic - not exposed to metal parts - because its an insulator
- plastic doesnt conduct electricity - no electric shock
- No earth wire just live and neutral
Why should you use a fuse with a rating a few amps above the recommended current?
It wont break under use.
If there is a surge, current increases a lot and will surpass the rating and break fuse
How do earth wires work?
- Earth wire connected to casing of appliance
- if live wire touches appliance casing, earth wire provides alternative pathway for electricity to flow
- no electric shock
Are all materials charged?
Yes, they have positive protons and negative electrons which cancel each other out. Most objects are overall neutral
What cant the electrons do on insulating materials
electrons cant flow back so transfer leaves a positive static charge on the one that lost electrons and a negative charge on the one that gained electrons
How would we know which way the electrons get transferred during static electricity?
Depends on the material
eg acetate rod loses electrons to cloth
What happens if an object keeps gaining negative electrons?
PD will develop between charged material and earth/earthed objects 0V
Large pd allows electrons to jump through air to earth = spark
How can cars build up charge?
Metal frame in contact with wind which can transfer electrons - shock
field lines always point from?
positive to negative charge
How does a negatively charged students receive an electric shock from touching a tap?
- there is a pd between the student and the tap
- which causes electrons to transfer from the student
- which earths the charge
1 Amp = how many mA
1 Amp = 1000mA
Why could there be a zero error on the ammeter?
ammeter displays reading when its not connected
Why wouldnt a touch work if the cells are the wrong way around?
- there is no current in a diode
- because diodie has a high resistance
Why does adding more resistors in parallel decrease total resistance?
- multiple paths for charge to flow
- total current is greater
Why could you still get an electric shock if the live wire is connected to the mains supply?
- live wire still carrying a 230 pd
- human is earthed
- so large pd difference between earthed human and wire
