P2 Flashcards
Negative and positive charges?
Negative charges can move, positive charges cannot. Negative attracts to positive, negative repels with negative, negative has no force with neutral.
Static electricity, how does it work?
When there is friction between two objects, electrons get transferred. The object that lost electrons now has a positive charge, and the other object has a negative charge. When the get near each other, the electrons suddenly get transferred, causing a spark. Or they get attracted. This is a non contact force
Drawing electric field diagrams
The arrows point in the direction that a positive charge would move if it was placed in the field
Electric current definition
The rate of flow of electrons
Circuit symbols!
Look in book 😝😔
What is potential difference?
Potential difference is the measure of the difference in potential energy between two points of the circuit. Measured in volts with a voltmeter.
Work done?
Work done =energy transferred
Resistance definition?
The measure of how hard it is for electrons to move in a circuit
What is a thermistor?
The resistance changes with the temperature. At low temperature- high resistance. As temperature increases, resistance decreases. Used in thermostats and heat activated fire alarms
What is a light dependant resistor (LDR🎀)
The resistance decreases as the light intensity increases
Low light levels, high resistance and low current
High light levels, low resistance and high current
Used to detect light levels
Series circuits?
-there is one path for electrons to travel through
-the potential difference is shared between components
-current is the same through circuits
Parallel circuits
-multiple paths for electrons to travel through
- potential difference is the same in all components
-current is shared between branches
RP3: characteristics of elements in a circuit at a constant temperature
Look in book! For graphs
-diode
-bulb
-resistor
Look in book for set up
RP1: how resistance depends on wire length
Method: connect a battery, ammeter and resistance wire and a switch. Voltmeter is in parallel with the resistance wire. Put a ruler under the wire to measure the length and use crocodile clips to change length. Measure the pd and current and calculate resistance
Result:the longer the length the higher the resistance
RP2: how the resistance of a circuit changes with the layout
Method: set up a series circuit with a battery, ammeter, switch, two resistors and a voltmeter in parallel to the resistors. Record the current and voltage . Set up in parallel, with one resistor on each branch. Record the current and voltage
Result:series circuit has more resistance
Direct current (DC)
An electrical current that always flows in one direction. Direct current is produced by cells and batteries
Alternating current(AC)
An electrical current that is constantly changing direction (60 times per second). Produced by generators and is used in mains electricity.
Oscilloscope graph labelling
Look in book!
Uk mains electricity: frequency and potential difference
Frequency: 50hZ
Potential difference: 230V
Three pin plug wires!
Live wire: on your right hand side of the diagram, connected to fuse.
Colour: brown
Function: the current enters device through this wire
Potential difference: 230V
Neutral wire: on your left hand side of the diagram
Colour: blue
Function: completes the circuit, connects the cable to the wall
P.D: 0V
Earth wire: in the middle of the diagram
Colour: green and yellow stripes
Function: provides an alternate path in case of a fault, prevents it becoming live
P.D: 0V(unless there is a fault)
How is the wire effective?
Core is made of copper; a good, ductile conductor
Wire is surrounded by insulation
How are the cases safe?
Made of plastic materials (insulation)
Why are the pins made of brass?
-good conductors
-ductile
-low cost
- good wear resistance
-doesn’t oxidise
-strong( won’t let wires become loose)
The national grid- transformers
Step up transformers:
-increases p.d, decreasing current.
-efficient because less energy is dissipated through heat in the power lines
Step down transformers:
-reduces voltage to 230V for home use(safe)
