Circuit investigations Flashcards
Why do we repeat readings
We repeat readings to find any anomalous results
Why do we calculate an average
We calculate an average from our repeated readings to eliminate the effect of random errors
Draw the circuit diagram for investigating current and voltage for a resistor
Include
Variable Power supply
Ammeter
Resistor
Voltmeter connected to the resistor in parallel
Switch
State the method for investigating current and voltage for a resistor
With the power supply off, set up the circuit
Increase the voltage, close the switch and record readings from the ammeter and voltmeter
Repeat this method, for higher voltages
Swap the connections of the power supply and repeat the whole experiment for negative values of current and voltage
Draw the graph for investigating current and voltage for a resistor
Straight line passing through the 1st quadrant and the 3rd quadrant
Voltage - on x-axis
Current - on y-axis
Using the graph, a conclusion for investigating current and voltage for a resistor
The graph is a straight line through the origin, therefore the current is directly proportional to the voltage (Current ∝ Voltage) - (as voltage doubles, current doubles)
This applies to both positive and negative values of voltage and current
This is true if resistance is constant
This is true for a resistor (and any conductor if its temperature is constant
Use the graph for investigating current and voltage for a resistor, to calculate resistance
Voltage = 10V
Current = 2.3A
E.g.
Go up from 10V until you hit the line - 2.3A
Voltage = 10V
Current = 2.3A
When voltage is 10, current is 2.3
Gradient = ∆y/∆x = 2.3/10 = 0.23 = I/V
Resistance = V/I = 1/gradient = 1/0.23 = 4.3Ω (to 1 d.p.)
Draw the circuit diagram for investigating the current and voltage for a diode
See book
Using a diode, how do you know which direction in which the current flows
The direction of the arrow of a diode represents the direction in which the current moves
State the method for investigating the current and voltage for a diode
Using the Potential divider, vary the voltage that the diode recieves
As the voltage is increased, record readings from the ammeter and voltmeter
To obtain negative values of current and voltage, swap the connections of the power supply
Draw the graph for investigating the current and voltage for a diode
Graph showing 1st and 2nd quadrants
https://bam.files.bbci.co.uk/bam/live/content/zwmb7p3/large
Draw the graph for investigating the current and voltage for a diode
Graph showing 1st and 2nd quadrants
https://bam.files.bbci.co.uk/bam/live/content/zwmb7p3/large
Using the graph write a conclusion for investigating the current and voltage for a diode
A diode only allows current to flow in one direction.
If the potential difference is arranged to try and push the current the wrong way (also called reverse-bias) no current will flow as the diode’s resistance remains very large.
Current will only flow if the diode is forward-biased.
When forward-biased, the diode’s resistance is very large at low potential differences but at higher potential differences, the resistance quickly drops and current begins to flow.
What is the threshold voltage - in terms of for investigating the current and voltage for a diode
The threshold voltage is the voltage when the current starts to flow
Name the graph with a straight line through the origin
The current-potential difference graphs for a resistor at constant temperature
Name the graph that curves - identify the component this relates with
Filament lamp
Name the graph where current is 0, then increases rapidly - identify the component this relates with
Diode
Describe the resistance of an LDR in the dark
In the dark, a LDR has a very high resistance
Describe the resistance of an LDR in light
In light, the LDR has a very low resistance
What is the LDR used for
The LDR is used as a light sensor
Describe the resistance of a thermistor when it is cold
When it is cold, the thermistor has a very high resistance
Describe the resistance of a thermistor when it is hot
When a thermistor is hot, it has a very low resistance
What are thermistors used for
Thermistors are used as a temperature sensor
Draw the symbols for:
switch (open)
switch(closed)
cell
battery
Diode
Resistor
Variable resistor
Lamp
Fuse
Voltmeter
Ammeter
Thermistor
LDR
LED
https://bam.files.bbci.co.uk/bam/live/content/z3cxgdm/large
Draw the circuit diagram for an automatic lighting circuit/system
Includes
Battery, LDR, Variable resistor, A bulb connected in parallel to the LDR
Explain how the automatic lighting circuit/system works
When it is light, the resistance of the light dependent resistor is low, therefore the voltage across it is also low
The bulb in parallel, with the light dependent resistor, receives the same voltage, and is therefore off.
When it is dark, the resistance of the LDR is very high, it therefore receives a much higher voltage, the bulb receives the same voltage and switches on
The variable resistor controls the sensitivity of the circuit, if it’s resistance is high, then it must be much darker for the light to switch on
