Paper 1 - 2a Electrical Circuits and Static Electricity Flashcards
Draw the circuit symbol for a lamp
an X in a circle
Draw the circuit symbol for a diode
An arrow head in a circle
Draw the circuit symbol for a resistor
A rectangular box
Draw the circuit symbol for a variable resistor
A rectangular box with a diagonal arrow
Draw the circuit symbol for an LED
Same as a diode with 2 arrows points away
Draw the circuit symbol for a fuse
A rectangular box with a horizontal one running through it
Draw the circuit symbol for a voltmeter
V in a circle
Draw the circuit symbol for an ammeter
A in a circle
Draw the circuit symbol for a thermistor
a rectangular box with a diagonal line through it
Draw the circuit symbol for an LDR
A rectangular box in a circular with 2 arrows pointing towards it
Which way does current flow in a circuit?
Positive to negative (anode to cathode)
Define current
Rate of flow of charge (electrons) measured in amps (A)
Define potential difference
work done / energy per unit charge (V = E/Q)
State the equation that links charge, current and time.
Charge = Current x time Q = It
What are the units of charge?
Coulombs (C)
What is the relationship between current and resistance?
As resistance increases, current decreases and vice versa
State the equation that links potential difference, current and resistance
Potential difference = current x resistance V = IR
State the units of potential difference
Volts (V)
State the units of resistance
Ohms (?)
State the relationship between the length of wire and its resistance.
As the length of the wire increases the resistance increases. They are directly proportional
As more resistors are added in series what happens to the total resistance?
Total resistance increases (Rt = R1 + R2 + …..)
State Ohm’s law
Current is directly proportional to potential difference constant temperature. this means resistance remains constant.
Sketch the I-V graph for a resistor
A straight line through the origin (current and potential difference are directly proportional - an ohmic conductor)
Sketch the I-V graph for a bulb
It starts off as a straight line through the origin but the the current levels offs so the graph curves. Non ohmic conductor
How does the resistance of a lamp change as it heats up?
As temperature increases resistance increases. Atoms/ions have more energy so vibrate more taking up more space making it harder for electrons to travel down the wire.
Sketch the I-V graph for a diode
Current can only flow in one direction. So zero current in the negative direction but in the positive direction current increases slightly after the origin. Non ohmic conductor
State the relationship between temperature and resistance for a thermistor
As temperature increases, resistance decreases.
State some uses of thermistors
In thermostats to turn circuits on/off if they get too hot to cold e.g. in an iron, hair straighteners etc
State the relationship between resistance and light intensity for a LDR
As light intensity increases, resistance decreases
State some uses of LDRs
In circuits to switch lights on when it gets dark
State the rule for current in a series circuit
Current - same flowing through each component
State the rule for potential differnce in a series circuit
P.d. of the power supply is shared between the other components
State the rule for current in a parallel circuit
Calculate current along each junction using I=V/R. Current across each junction adds together to calculate total current drawn from power supply.
State the rule for potential difference in a parallel circuit
Each junction has the same potential difference as the power supply across it.
State the rule for resistance in a parallel circuit
Resistance decreases in a parallel circuit. The resistance is always less than the smallest resistor.
Why does resistance decrease in parallel?
As more current is drawn from the power supply for the same potential difference. As R=V/I dividing by a larger current leads to a smaller resistance.
What happens when electrical current flows through a resistor?
Electrical energy is transformed into heat energy
What is a short circuit?
An electrical circuit that allows current to travel along unintended paths with no or very low resistance. Resistance low = current very high. This will cause the battery to overheat.
Why do lamps blow when they have just been turned on?
The lamp is cold so low resistance. As a result high current flows - sometimes enough to melt the wire in the bulb.
In a potential divider, what happens to voltage when two resistors are equal?
They share applied voltage equally
In a potential divider, a current passes through a resistor then through a thermistor. How does the voltage across each component change as temperature decreases?
The thermistor cools. The resistance of the thermistor rises, taking a larger share of input voltage. As the input from the battery is constant so output voltage rises across the fixed resistor.
In a potential divider, a current passes through a resistor then through a thermistor. How does the voltage across each component change as temperature increases?
The thermistor heats up. The resistance of the thermistor decreases, taking a smaller share of input voltage. As the input from the battery is constant so output voltage decreases across the fixed resistor.
In a potential divider, a current passes through a resistor then through an LDR. How does the voltage across each component change as light intensity increases?
If light intensity increases the resistance of the LDR decreases. The LDR will take a smaller share of the input voltage. As the input voltage from the battery is fixed the output voltage across the fixed resistor must increase.
In a potential divider, a current passes through a resistor then through an LDR. How does the voltage across each component change as light intensity decreases?
If light intensity decreases the resistance of the LDR increases. The LDR will take a larger share of the input voltage. As the input voltage from the battery is fixed the output voltage across the fixed resistor must decrease.
What objects can create an electric field?
Any charged object
How is the strength of the electric field related to the distance from the object?
The further away from a charged object the weaker the field
what is the name of the force when charged objects attract or repel each other? is this a contact or non contact force?
Electrostatic attraction/repulsion. It is an example of a non contact force
Sketch the field lines around a positive charge.
A radial field with the arrows pointing away from the charge
Sketch the field lines around a negative charge.
A radial field with the arrows pointing towards the charge
How are static charges created?
Insulating materials are rubbed against each other. The force of friction can run electrons onto or off the material.
If an insulator gains electrons what happens to its charge?
It becomes negative
If an insulator loses electrons what happens to its charge?
It becomes positive
If two positive charges are close to each other, what will happen?
They will repel
If two negative charges are close to each other, what will happen?
They will repel
If a negative and a positive charge are close to each other, what will happen?
They will attract
What happens to an object that is isolated from the earth if a static charge builds up?
As static charge builds up the potential difference on the object increases. Eventually the p.d. gets so large that the charge can jump from the object to the earth in the form of spark.
What do electric field lines show us?
The closer the lines the stringer the field/force. If the line get further away from each other the field/force gets weaker. The arrow heads show the direction of force a positive charge would feel.
What is an electric field?
The region where a charged object would experience a force
