Topic 5 - Electricity and Circuits Flashcards
(49 cards)
How do you measure voltage
current x resistance
What is meant by potential difference
driving force which pushes the charge around
higher the PT the higher the current
How do you measure current
Potential difference / resistance
What is the current
Flow of electric charge (electrons) around a circuit and it will only flow if theres a potential difference
What is resistance
anything that slows the flow down
usually increases with temperature
How do you measure charge
current x time
What is charge
current is the rate of flow of charge.
its a flow of electrons
Describe the current and potential difference in a series circuit
Current is the same everywhere
PT is shared between each component
How does the Resistance change in a series in you add a resistor
It increases
Describe the current and potential difference in a Parallel circuit
Current is shared at junctions/branches
potential difference is the same across all components
Why does resistance increase with temperature
because the electrical charge has to do work against the resistance
as the current flows through a resister it heats up because the electrons are colliding with ions in the lattice resistor
-If resistor too hot no current will flow (unless thermistor)
How could you investigate a component in series
-connect a voltmeter in parallel with the component you’re investigating and ammeter in series
-change the potential difference on power supply and take several readings from the ammeter and voltmeter
for different output voltages
-Plot I-V graph to work out resistance
(make sure circuit doesnt overheat)
What would you find if you swapped the direction of a diode
current cant flow through anymore
What would you find if you kept the PT of a thermistor the same but gradually increased the temperature
that as the temperature increases the current through the resistor decreases and the resistance decreases
Describe a test for a LDR
Carry out in dim room
- keep PT constant but slowly adjust the light level near the LDR and measure the current through LDR
- should find as light intensity increases, current increases and resistance decreases
Describe an IV graph for Resistors and wire
current is directly proportional to PD so straight line
Describe an IV graph for a Filament lamp
Increasing current increases temp which makes resistance increase so theyre curved
Describe an IV graph for a diode
current only flows through a diode in one direction
diodes have high resistance in opposite direction
(so flat line and then sudden increase)
What is an LDR and name some uses
Light dependent resistors
- in bright light resistance falls so current increases
- used for automatic night light lights and burgler detectors
What is a thermistor and what is it used for
hot conditions resistance drops
-used in temperature detectors eg) electric kettles
car engines
How does resistance change in a series and parallel when you add a resistor
Series- increases resistance- makes resistors have to share PD
Parallel - decreases total resistance as both resistors have same PD and by adding another loop for resistor you are giving the current another direction so increase in current= decrease in resistance
How can we find the energy transferred in a system with a formula?
Current x Potential Difference x time
Explain why the transfer of energy leads to heating
Because as energy is transferred some is as thermal energy to thermal stores as heating usually increases resistance. so its dissipated to surroundings
How is efficiency effected by heating
it decreases
