P3 Flashcards
What is electric charge
A property of a particle - can be positive or negative
What happens when you rub two insulators together
Electrons can be transferred
One insulator ends up with more electrons than the other giving it an overall negative charge
What is static electricity
The charge insulating objects acquire due to the transfer of electrons
How do you discharge an object
Connect it to something that allows a current to flow (conductor)
What are sparks
A flow of current and lightning through the airb
What is an electric field
A field around a charged particle that will attract or repel another charged object even if they are not touching
What is current and how do you meausrebit
Current is the rate of flow of charged particles
How do you make current flow
You need a complete circuit containing a cell or battery
How does the rope model, model electricity
A person pulling the rope is a battery and the movement of the rope is the charge
The person griping the rope represents a circuit component
What is conventional current
Positive to negative flow of charge
This is opposite to electron flow
How do you calculate charge
Charge is measured in Coulombs
Charge = current. × time
What is potential difference
A difference in electrical potential produced by the separation of charge
1v shows 1J of energy transferred per coulomb of charge that is moving through the circuit
What happens when you apply p.d to two sides of a wire
An electric field is created quickly, so the charged electrons move straight away
In a diagram what end of a cell/battery is positive and which is negative
Positive - the longer line
Negative - the smaller line
How d measure the energy transferred (electrical working) by p.d
P.d (volts) × charge
What is a series circuit
A circuit with one loop
The current is the same throughout all of this loop
How do you measure amps
Using an ammeter
How do you measure volts
A voltmeter
What does a voltmeter measure
Volts - the rise in potential across a cell or battery / the drop in potential across a component
How do voltmeters need to be set up in order to show the p.d of a component
Connected to both sides of the component
How do you find the voltage at the cell of a series circuit
Add all the voltage (from the components) together
Why is the voltage across a wire zero
There is a very little potential difference across wires
What is a parallel circuit
Having two or more loops
What is resistance
A measure of how easy it is for current to flow
How do you calculate restistance
Using
Resistance = p.d ÷ current
R= v/I
How do you calculate p.d
V = I×R
Amps is I
Why does the resistance of some components change
Metals are made of positively charged ions in a regular shape
These ions are formed when electrons leave the outer shell - and these delocalised electrons move throughout the metals structure
Resistance is produced when electrons collide with the ions in a lattice. This is why the resistance of some components change with current
(Greater current = faster electrons = more collisions)
What is a variable resistor
A resistor that can change the amount of wire or other resisting material - to increase or decrease a circuit resistance
Do longer wires have a greater or lower resistance
The longer the wire the greater the resistance
What can you use a p.d and current graph to calculate
The resistance
What does the graph of a wire or resistor look like
It is a linear graph where the p.d is directionally proportional to the current
What is ohms law
The current is directly proportional to the potential difference if the current doesn’t change
The resistance is constant
What does a p.d current graph of a wire look like
Its a non linear graph
This is because the wire gets hot, so the resistance is not constant
How do filament lamps work
Electrons in a wire collide with ions in a wire.
The ions vibrate more as the temperature gets hotter
(As the temp increases a glow is produced)
As that happens there are more collisions
The wire heats up more.
The current increases qs p.d increases but at a slower rate
What does the current p.d graph of a diode look like
Diodes only work in positive values, so when charge in negative no current is produced
When you apply a small amount of positive p.d the current suddenly increases
How is an LED connected to a battery
The long leg of an LED is connected to a battery
What is a thermistor
A circuit component that has a resistance which depends on temperature
Its a semi conductor
Resistance decreases when temp increases
(Explanation - not needed)
Increased temp = increased conduction = increased flow of electrons
How does the resistance change with temperature
As the temperature increases the resistance increases
How could a thermistor be used in a circuit with a fan
As the outside temperature increases the resistance increases. This means the current must be increasing (to keep p.d the same)
This current can then activate the fan (if the fan only turns on above a certain current)
What is an LDR
A light dependent resistor
Its resistance depends on the light intensity
How does the resistance of an LDR change with LI
As light intensity increases, more electrons are released by the semiconductor so resistance decreases
(Same for Thermostor)
How do you calculate net resistance
It is the total resistance in a circuit
Adding components in series increases the net resistance
Adding components in parallel decreases the net resistance
What are sensing circuits
A circuit which contains a conductor with a resistance that changes with a change to the environment
How do you calculate electrical power
Power = p.d × current
Power = resistance × current^2
How do you calculate energy transferred (using power)
Power × time
What happens to current and voltage in series circuits
Current - the current is the same across the whole cell
P.d (voltage) - The p.d is split across each component in the circuit.
This voltage adds up to the p.d across the battery
What is current and p.d like in parallel circuits
Current - The current in each branch (loop) adds up to the current at the battery
P.d - the total voltage in each loop is equal to the voltage at the battery
What is direct current
Current in a cell moving in one direction
What is alternating current
Current in a circuit that is constantly changing at a specific frequency
What is the voltage and frequency of alternating current in the uk
Frequency - 50 hertz
Voltage - 230v
What device is used to view changing p.d
An oscilloscope
What is an oscilloscope used for (p3)
It can be used to measure alternating current.
It shows a graph of p.d against time, where the p.d is constantly changing between positive and negative values
How do you calculate resistance in parallel
Total resistance = 1/r1 + 1/r2 ….
