p2 Flashcards
what happens if you close an open switch
electrons flow out of the cell and move around the circuit to the negate end to positive
what do u call a flow of electrons
an electric current
what is a series circuit
when it has no branches
what is a current
a flow of electrical charge around the circuit
what is the unit of current
ampere amps A
how do we measure a current
with a ammeter
what is the same in a series circuit
the current is the same all the way around
what do u call it when scientist draw the current in th e opposite direction
the conventional current
what dose a parallel circuit contain
branches
what dose the branches mean in a Parallel Circuit
that the current splits
Work out the current leaving the cell in a parallel circuit
0.7 amps
What are circuits like this called
Series circuit because it has no branches
What dose the current in the branches add up to in a Parallel circuit
Adds up the total current leaving the cell
What is the energy transfer in this circuit
The cell stores a chemical energy the. Is transferred to the electrical energy which is carried by the electrons passing out the cell when it passes through the lamp it’s transferred to a different energy in the lamp it’s light energy and thermal energy
What is the energy transfer in this circuit
The cell stores a chemical energy the. Is transferred to the electrical energy which is carried by the electrons passing out the cell when it passes through the lamp it’s transferred to a different energy in the lamp it’s light energy and thermal energy
What is potential difference also known as
Voltage
What does the potential difference of 1 volt tells us vine
That there’s 1. Joule of energy is transferred for each coulomb of charge that is moving through the circuit
What is pd measured with
A volt meter
Are the lights dimmer or lighter in this circuit
Dimmer
Describe the energy current between this two lamps
The total energy carried by the current has been shared between the two lamps
What has to add up in this circuit
The two lamps is the same as the p.d across the cell
Describe what’s happening in this cell
The cell has a pd of 9 volts which means that 9 joules of energy is transferred fir every coulomb of charge then is shared between the two lamps the p.d of 6 volts will be more
Is the pd in parallel circuits the same
Yes the volt between each component is the same
What is the pd across the bottom lamp in the parallel circuit
Pd is 2 volts
A cell has a pd if 9 volts what will it be if we add a battery
You will do 2 x 9 = 18
18 volts
A cell has a pd if 9 volts what will it be if we add a battery
You will do 2 x 9 = 18
18 volts
1 cell is = to 9 volts work out the pd of the battery
Volt of the battery = 0
It cancels out
What is the pd of the battery 1 cell = 9 volts
It will be 9x 2 = 18 but one cell is facing the wrong direction which will cancel out one of the cells = only 9 volts
What is electrical charge measured in
Coulombs (C)
What does a current of 1 ampere =
1 coulomb of change flowing per second
The size of electrical current is the
Rate flow of electrical charge
What equation do we use to work out the charge flow in a circuit
H
What equation do we use to work out the charge flow in a circuit
H
0,3 x 20 =6c
What is the calculation of energy transfer
25 + 5 = 30
5 x 3 = 15 joules
What does the resistance tells us
How much energy is required to push coulomb of charge through
What’s the difference between lamp A and lamp B
I’m lamp a it has a low resistance but lamp b has a high resistance
What’s the equation for resistance
What is the resistance of the lamp
10 divided by 1
The pd divided by the current = 10
What is the equation to work out the pd needed to produce a certain current
What happens to the electrons when they move through a conductor
They collide with atoms in the metal
The higher the resistance
The more energy is transferred as the current moves
Is a lot of energy wasted in resistance
Yes
What do we use when we want to add resistance into a circuit
To do that we use a resistor
What do we do if we wanted to make the lamp dimmer
We could add a resistor the pd is shared between the lamp and resistor less electrical energy going to the lamp
What does the A mean
Current
What does the v mean
Potential difference
C & v
Currrent volts
Does the resistance change if we increase the current
No the resistance is constant
What is it called when a resistor is constant
An ohmic conductor
The resistance will only stay constant if the ……
Temperature is constant
What does filament mean
A very thin wire
During electrical current passes through the filament lamp the wire gets
extremely hot causing it to give out light
What type of graph do we get from changing the pd of the filament lamp and measuring the current in a circuit
It’s not directly proportional to the pd
What type of graph do we get from changing the pd of the filament lamp and measuring the current in a circuit
It’s not directly proportional to the pd
Why was the filament lamp directly proportional
Because the filament gets hot causing the resistance to increase
At high temperatures the atoms and the filament
Vibrate more that means the electrons and current now collide more with the atoms more energy is push the current through the filament
Describe what’s happening in the graph
As the pd increases the current no longer increases as much which feels us that resistance is increasing
Is a filament lamp a ohmic conductor
No it’s not it’s not constant
What way dose the current flow through a diode
At one direction only due to the diode having a very high resistance in the reverse direction
Explain what’s happening to the diode here
The cell is turned and the cell is now flowing in the opposite direction that’s means the diode will now all the current to pass through due to the diode high resistance in the reverse direction
For the graph diode can current flow on the opposite direction
No it’s can’t
The graph for diode
What are diodes useful for
For controlling the flow of current in circuits
Where are leds found in
Tv ligh flash light bulb
Where are leds found in
Tv ligh flash light bulb
What does led stand for
Light emitting diode
An led only flow In
One direction as like the diode
What dose an led gives off
It gives off light when a current flows through
What do resistors in series do
Add together
What dose LDR mean
Light depending resistor
In the light the resistance of the LDR
Is very low
The graph for LDR
Low light intensity high resistance
High light intensity low resistance
The graph for LDR
Low light intensity high resistance
High light intensity low resistance
The graph for LDR
Low light intensity high resistance
High light intensity low resistance
What’s happening hereb
In the light when the phone is not held to tor ear is resistance of the LDR is very low which mean it takes very little energy to pass through the LDR because of The pd across the ldr is very low ( takes very little energy to pass through for the current to pass through the LDR )
The pd is shared between components in
Series so that means the pd across the lamp is large the lamp now lights up the scream
What happens if the phone is held to your ear
The LDR is in darkness the resistance of the LDR rises sharply now. It takes a great deal of energy for the current to pass through the LDR so the pd across the LDR is very high which mean less electrical energy is available for the lamp the pd across the lamp is low the lamp becomes very dim Thai turns the scream off
The resistance of the thermistor decreases if the temperature
Increases
The resistance of the thermistor decreases if the temperature
Increases
What’s happening here
Under cool condition the thermistor is high it takes a lot of energy for the current to pass through the thermistor the pd across the thermistor is high the pd across the fan is small
What’s happening here
If the computer gets hot the resistance of the thermistor falls now It takes much less energy fir the current to pass through the thermistor this mean the pd across the thermistor is low so. more electrical energy is is available for the fan which makes the pd across the fan very high so the fan powers to high speed and cools the computer down
How do we increase the length of the wire practical 3 resistance
We attach the wire to a meter ruler using tape now we connect the wire to the rest of the circuit using 2 crocodile clips only the one with the two crocodile clips is connected to the circuit we can move it further away now we can change the. Length of the wire and measure the resistance in the circuit
What is the graph for required practical 3
The wire is Directly proportional to the length
What are the issues about practical 3
If we look at the graph there’s a small resistance when the length of the wire is zero and that should not be there which is not an actual result called a zero error
What is a zero error
Is a reading on a measuring instrument when the value should be zero
It’s a systematic error we cannot reduce it by carrying out repeats
In the case of resistance we need to subtract the zero error form all our readings
What is the zero caused by in the practical 3 resistance
It’s caused by the requirement it’s extremely difficult to get the crocodile clip at the zero position on the ruler
There also come resistant caused by the contact between the crocodile clip and the wire ( nothing we can do )
What is the other affect in the practical 3 resistance other than the zero effect
Is the heating effect
If the temperature of the wire increases than the resistance will also increase
What can we do to stop the heating effect
We can use a low pd this will keep the current low reducing any heating in the wire
We should only turn on the current when were taking a reading
Turn off current between readings
How do we increase the resistance in a circuit
By using a longer wire
What does a variable resistor contain
A long piece of wire and a coil
