P4 Good One Flashcards
What is the only thing that can be transferred from atom to atom ?
Only electeons can be transferred to or from an atom
How can you charge an object (give it an overall positive or negative charge) ?
Charging by friction, from rubbing insulating materials together. Negatively charged electrons are rubbed off one material and onto another.
What is the force between 2 charged objects and why does this force happen ? What does the force cause and what happens if you increase the distance between the charged objects ?
When a charged object is placed in a electric field of another object, it feels a force
Two charged objects exert a non-contact force on each other because of the electric fields interacting with each other
The forces cause an attraction or repulsion
As you increase the distance between the charged objects, the strength of the field decreases and the force between them gets smaller
How can you draw lines to represent a positively or negatively charged electric field?
You would draw a charged metal sphere and if its a positively charged sphere you would draw the lines pointing away from the sphere and if it was a negatively charged sphere then you would draw the lines going in towards the sphere.
What would happen to the electrons in the air molecules if there is 2 oppositely charged objects ?
If the two objects are oppositely charged, electrons in the air molecules between the two objects experience a force towards the positive object.
If the field is too strong, sparking happens, because some electrons are pulled out of air molecules by the force of the field. These electrons hit other air molecules and knock electrons out of them, creating a sudden flow of electrons between the two charged objects.
What do like charges do ?
Like charges repel
What do unlike charges do ?
Unlike charges attract
What does a cell do ?
A cell is necessary to push electrons around a complete circuit. A battery consists of two or more cells. The + symbol next to the long line of the cell indicates that this is the positive terminal of the cell
What does a switch do?
The switch enables the current in a circuit to be switched on or off
What does a battery consist of ?
A battery consists of 2 or more cells
What does an indicator do?
An indicator, such as a bulb, is designed to emit light as a signal when a current passes through it .
What does a diode do?
A diode allows current through in one direction only
What does a light emitting diode do ?
A light emitting diode (LED) emits light when a current passes through it
What does an ammeter do?
Am ammeter is used to measure electric current
What does a fixed resistor do?
A fixed resistor limits the current in a circuit
What does a variable resistor do?
A variable resistor allows the current to be varied
What does a fuse do?
A fuse is designed to melt and therefore ‘break’ the circuit if the current through it is greater than a certain amount
What does a heater do?
A heater is designed to transfer the energy from an electric current to heat the surroundings
What does a voltmeter do?
A voltmeter is used to measure potential difference (voltage)
What is an electric current ?
An electric current is the flow of charge
What is the size of the current
It is the rate of flow of the electric charge
The bigger the number of electrons that pass through a component each second …..
The bigger is the current passing through it
In a circuit that is a closed loop, the current at any point is the
Same as the current at any other point in the circuit. This is because the number of electrons per second that pass through any part of the circuit is the same as at any other part
What is charge flow measured in ?
In coulombs (C)
What is electric current measured in ?
In amperes (A) or sometimes abbreviated as amps
What is the formula for charge flow (electric charge) ?
Charge flow (C) = Current (A) x time taken (s)
How is a filament lamp in a circuit turned on ?
Electrons passing through a battery gain energy from chemical reactions in battery,
electrons transfers energy to filament bulb by colliding with atoms in filament as it passes through,
transfers some energy to atoms in wire in same way
What is the definition of current ?
Current is the flow of charge (electrons) - electrical charge will only flow around a complete (closed) circuit if there is a potential difference. So a current will only flow is there is a source of potential difference.
Where does current flow from and to ?
Current flow from positive to negative terminals
What is potential difference (or voltage) ?
Potential difference is the driving force that pushes charge around the circuit as charge will only flow if there is a potential difference
What is the unit for potential difference ?
Volts, V
What is resistance ?
Resistance is anything that slows the flow of charge
The greater the resistance over a component …….
The smaller the current that flows across it (for a given amount of pd across the component)
More electrons pass around a circuit when…..
A larger current flows
Whats the equation that links pd, current and resistance ?
Pd (V) = Current (A) x resistance (omega symbol)
What does the resisitance of a circuit depend on ?
The resistance of a circuit depends on a number of factors: whether components are in a series or parallel circuit, or the length of wire used in a circuit
What does the ammeter do and where does it have to be placed ?
Measures the current (amps) flowing through the wire
Must be placed in series with whatever your investigating
What does the voltmeter do and where does it have to be placed ?
It measures the pd across the wire (in volts)
It must be placed in parallel around whatever you’re investigating - NOT around any other bit of the circuit, e.g. the battery
How do you carry out the ‘effect of wire length on resistance’ RP
1)Attach a crocodile clip to the wire level with 0 cm on the ruler.
2)Attach the second crocodile clip to the wire, e.g. 10 cm away from the first clip. Write down the length of the wire between the clips.
3) Close the switch, then record the current through the wire and the pd across it.
4) Open the switch, then move the second crocodile clip, e.g. another 10 em, along the wire. Close the switch again, then record the new length, current and pd.
5) Repeat this for a number of different lengths of the test wire.
6) Use your measurements of current and pd to calculate the resistance for each length of wire, using R = V ÷ I (from V = IR).
7) Plot a graph of resistance against wire length and draw a line of best fit.
8) Your graph should be a straight line through the origin, meaning resistance is direcfly proportional to length the longer the wire, the greater the resistance.
What is omhs law?
The current through a resistor at constant temperature is directly proportional to the potential difference across the resistor.
Filament lamp - current against resistance explain ?
When an electrical charge flows through a filament lamp, it transfers some energy to the thermal energy store of the filament, which is designed to heat up. Resistance increases with temperature, so as the current increases, the filament lamp heats up more and the resistance increases
Diode - current against resistance - explain
For diodes, the resistance depends on the direction of the current. They will happily let current flow in one direction, but have a very high resistance if it is reversed.
How to do the components i-v charateristic RP ?
1) Begin to vary the variable resistor. This alters the current flowing through the circuit and the potential difference across the component.
2) Take several pairs of readings from the ammeter and voltmeter to see how the potential difference across the component varies as the current changes. Repeat each reading twice more to get an average pd at each current.
3) Swap over the wires connected to the battery, so the direction of the current is reversed.
4) Plot a graph of current against voltage for the component.
What is charge (flow) ?
The charge is the current flowing past a point in a given time. Charge is measured in coulombs (C).
What is an LDR and what does it do?
LDR is short for light dependent resistor
In bright light the resistance falls
In darkness the resistance is highest
They have lots of applications like automatic night lights or burgular detectors
What is a thermistor and what does it do ?
A thermistor is a tempertaure dependent resistor
In hot conditions, the resistance drops
In cool conditions, the resistance goes up
Used for things like car engine temperature sensors or electronic thermostats
What happens in a series circuit if one component stops working ?
Once one of the components is broken then all the components will stop working.
What is the potential difference rule for a series circuit ?
In series circuits the total pd of the supply is shared between all the components.
So the pd round a series circuit always adds up to the source pd
V total = V1 + V2 +….etc
What is the current rule for a series circuit ?
The current has the same value everywhere in a series circuit
The size of the current is determined by the total resistance of the circuit and by the total pd of the cells - I = V/R
I1 = I2 = …..etc
Whats the rule for resistance in a series circuit ?
In series circuits the total resistance of two components is just the sum of their resistances:
R total = R1 + R2
This is because by adding a resistor in series, the two resistors have to share the total pd.
The potential difference across each resistor is lower, so the current through each resistor is also lower. In a series circuit, the current is the same everywhere so the total current in the circuit is reduced when a resistor is added.
This means the total resistance of the circuit increases.
The bigger a component’s resistance, the bigger its share of the total potential difference.
In a parallel circuit what happens if one of the components breaks ?
It would hardly affect the others at all
Whats the rule for pd in a parallel circuit ?
The pd is the same across all components so all components get the full source pd
V1 = V2 =……etc
What is the rule for current in a parallel circuit ?
Current is shared between the branches
In a parallel circuit, the total current flowing around the circuit is equal to the total of all the currents throught the separate components
Or in other words, the total current is the total of all the currents through all the components
I total = I1 + I2 + ….etc
What is the rule for resistance of a parallel circuit ?
Adding resistors in parallel reduces the total resistance
Investigating resistance RP
In a series circuit, adding resistors will increase the total resistance of the circuit and therefore decrease the total current through the circuit
In a parallel circuit, adding resistors wil, decrease the total resistance of the circuit and therefore increase the total current through the circuit
What does the force on an charged object in a electric field depend on ?
The force on a charged object in a electric field depends on the strength of the electric field that it’s in
