Topic 10- Electricity and Circuits Flashcards
What is potential difference?
- Diference of potential electrical between two points
- How much (energy) is used in a component
- Energy carried by electrons
What is current?
-Flow of electrons
- From positive to negetive…
What is a volt in coulombs?
Joule/coulomb
- potential difference is how much energy transfered per unit of charge/ current
Charge =
Current x time
Energy =
charge x potential difference
number of electrons x how much energy transferred to components
Why does potential difference cuase flow of electrons
where is current conserved?
current is conserved at a junction in a circuit
What does a variable resistor work?
- Lengthens wire and increases resistance
- Decreases current
Voltage =
Resistance x Current
What is current measured in?
-I
-Amps
What is Voltage measured in?
-V
-Volts
What is charge measured in?
-Q
-Coulumbs
What is energy measured in?
-E
-Watts
What is resistance measured in?
-Ω
-Ohms
Potential difference series?
- Split
- All components only have enough energy as batterty
Current series?
- Same everywhere
- Only one way electrons can flow
Resistance series?
- Added together
- One electron flow so all encounter same resistance
Potential difference parallel?
-Same everywhere
- Current and resistance are indirectly proportional, keeping voltage the same
-choose path of least resistance
-But more electron flow cuases higher resitance
-so overall less r and more I
-or more r and less I
-V= IR
Current parallel?
- Different
- They choose path of least resistance
Resistance parallel?
- Different, cannot add
- 1/R1 + 1/R2 + 1/R3
-Cuase not all resistance is in the same route
Why does net resistance decrease in parallel?
- Adding another pathway for electrons
- (3 resistors in series vs 3 resistors in parallel)
- (electrons go through all 3 vs just one per route)
Core Practical: Construct electrical circuits to:
a) investigate the relationship between potential difference, current and resistance for a resistor and a filament lamp
1) Variable resistor: changes voltage by changing resistance
2)Ammeter: Take readings of current
3)Volmeter: Take reading of voltage across the fixed resistor
4) Fixed resistor: Investigate how higher volt supply changes current if resistance does not change
Independant: Voltage (variable resistor)
Dependant: Current
Control: Same components/fixed resistor and power supply
Core Practical: Construct electrical circuits to:
test series and parallel circuits using resistors and filament
lamps
RESULTS
-Attach 2 lamps in series with ammeter and volmeter
-Take readings
-Repeat in parallel circuit
* - Brighter in parallel as there are more routes for electrons and therefore less resistance
How does current vary with potential difference for a filiment lamp
relating to its resistance?
Describe graph and explain
- slight S shape
- When more V is supplied it is brighter and hotter
- Heating effect cuases more resistance meaning less current
How does current vary with potential difference for a diodes
relating to its resistance?
- Flat line and sudden rapid increase at 0.6-0.7 v
-As Voltage increase
-Resistance decreases rapidly
-Causing current to rapidly increase
How does current vary with potential difference for a fixed resistors
relating to its resistance?
- Directly proportional
- Resistance is fixed
What is an ohmic conductor?
Current and voltage are directly proportional if temperature is constant
How does resistance change with brightness of an LDR
- Higher resistance when dimmer
- Lower resistance when brighter
How does resistance change with temperature of an thermister
- Higher resistance when coldere
- Lower resistance when hotter
Experiment to find relationship witth volts and current of a resistor or filiment lamp:
-Battery: supply potential difference
-Ammeter: current
-Volmeter: across the resistor/ lamp
1) Note down readings
2) Variable resistor: changes resistence and therefore voltage
3) Reverse battery/ current for negative readings
Experiment to find relationship with volts and current of a resistor: PROBLEM and SOLUTION
- Get too hot/heating effect increase resistance
- Don’t leave circuit on for too long
Why do we use a fixed resistor in a circuit with a diode?
- Diodes easily damaged by high current
- extra resitor keeps current reletively low
What and why do we use instead of an ammeter for diode experiment?
- Miliammater (reads smaller currents)
- Low current (extra reistor)
Experiment to find relationship witth volts and current of a Diode:
Same as + what is extra
- Same as resistor/ filiment lamp
- Use extra resistor and a miliammeter
- there will be no readings for reveresed current
What is the heating effect?
Resistance cuases electrons to transfer energy in the form of heat
How to reduce energy loss in circuits?
- Low resistance wires
- Insulate wires
Why do hotter wires cuase higher reistance?
-Ions vibrate more
-More likely to collide with electrons
Heating effect posisitves/ Uses?
-Kettle
-Domestic heating
-Electric ovens/ toasters
electrical work —> thormal store
Heating effect disadvantages?
- Energy loss
- Fire hazard
Energy =
current
Current x Time x Potential difference
E= I x t x V
What is power
Rate of energy
Energy transferred per second
Power=
Energy/ Time
P = E/T
Power =
Current
Current x Potential difference
P = IV
Power =
Current ^2 x resistance
P= I^2 x R
Direct vs Alternating current: voltage
-Direct: voltage remains the same
-Alternating: Voltage switches between positive and negative
What supplies + what is direct current?
- Battery/ Cell
- Current moves in one direction only
What is an alternating current?
- Charge movement changes direction
Uk domestic supply: Curent, Hz and voltage
- a.c (alternating)
- 50Hz (alternates per second)
- 230 V
What does the live wire do?
- Supplies alternating potential difference of about 230 volts
Live wire colour?
Brown
Neutral wire colour?
Blue
Earth wire colour?
Green and yellow striped
What does the neutral wire do?
- Completes the circuit
- Carries away current (out/ back into mains)
Earth wire and Neutral wire potential difference
0 volts
What does the Earth wire do?
- Stops the casing from becoming live
- By allowing an alternate pathway for the current to flow
What are wires made of?
-Copper
Why should a fuse and switch be attached to the live wire?
- To break the connection to the mains supply (fuse melts due to too much current heating it up, as it has a low melting point)
- Stop the casing becoming ‘live’
Why is the earth pin longer?
-Connects with the socket first
-Provides alternative pathway incase live wire is broken
What would happen if the live and Earth wire touched?
- Direct circuit between the Earth and 230v
- Could cause a fire or shock
Which domestic electrical appliances have higher power ratings?
Thermal apliances (kettle/oven vs fan)
What do power ratings show?
Energy it transfers/ work done per second
