circuits Flashcards
What are differences between series and parallel circuits
Series
- different component are connected
- current is same everywhere
- if you remove or disconnect one component, the circuit is broken
Parallel
- each component is separately connected
- if you remove or disconnect a component, it will hardly affect others at all
Current is shared
What is a voltmeter and what is it used for
Connected in a parallel with a component to measure the potential difference in volt, across it
What is potential difference
Energy transferred per unit charge passed and hence that volt is a joule per coulomb
What is the equation for energy transferred
E =QxV
energy transferred (joule, J) = charge moved (coulomb, C) ×
potential difference (volt, V)
What is an ammeter and what is it used for
Connected in series with a component to measure the current in amp in the component
What is electric current
Current is the flow of electric charge around a circuit. Current will only flow through an electrical component if there is a potential difference across the component and if the circuit is complete.
The current flowing through component depends on the potential difference across it and the resistance of a component
What is the equation for charge
Q = I x t
charge (coulomb, C) = current (ampere, A) × time (second, s)
What is conserved where in a circuit
At a junction
How does a variable resistor change the resistance and the current?
A variable resistor to change current through the circuit. Increasing the total resistance by increasing the variable resistance resistance lowers the current through the circuit. This also changes potential difference across the test component.
Equation for potential difference
V = IxR
potential difference (volt, V) = current (ampere, A) × resistance
(ohm, Ω)
If two resistors are in a series, why is the net resistance increased?
In a series current flows in One Direction
If two resistors are added, this means the resistant force is bigger than the current and therefore the current can’t overpower the resistance so resistance is increased
Why with two resistors in a parallel the net resistance is decreased
In a parallel circuit, the current flows different ways and is shared
B both resistors have the same potential difference across them as the source this means the pushing force making the current flow is the same as the source potential difference for each resistor you add
By adding another loop that the current has more than One Direction to go in
This increases total current that can flow around the circuit
How to test series in parallel circuits using resistor and filament lamps
Set out the circuit
Very the output potential difference from the power supply. Record the readings from the ammeter and volt meter for each change.
Replace the resistor with filament lamp and repeat step two
Now connect to 2nd filament lamp to the circuit in parallel to the first . Connect our metres on the 2nd V meter.
Again, very the output potential difference of the supply
For a Siri circuit, you should find that as the potential difference increases the current through the resistor increases
For the parallel circuit, you should find that as potential difference increases so does the current through each bulb . The potential difference across each bulb is the same as the potential difference of the power supply you should also know that the total current through the circuit is the sum of the current for two branches and this is larger than the total current through the series circuit with one filament bulb
how to investigate the relationship between potential difference, current and resistance for a resistor and filament lamp
Connect the circuit - the ammeter and component are in series, which means they can put in any order in the main circuit (the voltmeter must be in parallel around the component under test)
Change the resistance of the variable resistor. Measure the current through and potential difference across the component.
Take several pairs of readings from the ammeter and volt meter at a number of different resistances
Plot the current against the potential difference to gain an IV graph
You can use the state to work out the resistance for each measurement of I and V
Make sure the circuit doesn’t get too hot , if it does disconnect it for a while between reading so it can cool down
How does current vary with a diode with potential difference and how it relates to resistance?
After you finish taking measurements for a range of current, remove the diode and swap its direction. You should find that current cannot flow through the diode anymore.
How does current vary with a thermistor with potential difference and how it relates to resistance?
Keeping the resistance of the variable resistor constant, gradually heat the thermistor. You can do this by placing the thermistor against a beaker of hot water. You should find that as the temperature increases, the current through the thermistor increases as the resistance decreases.
How resistance of a light dependent resistor varies with light intensity?
Conductor experiment in a dim room. Again keep the resistance of the variable resistor constant and slowly adjust the light level near to the LDR. You should find as the light level gets brighter, the current through the LDR increases as the resistant decreases.
How does the resistance of a thermostat varies with change of temperature?
A thermistor is a temperature dependent resistor
In hot conditions, the resistance drops
in cold conditions. The resistance goes up.
The thermistor make useful temperature detectors, i.e. car engine temperature sensors, and electronic thermostats
When there is an electric current in a resistor, what happened?
There is an energy transfer which heats the resistor
When electrical energy is dissipated as the more energy in the surroundings, how does the electrical current work against electrical resistance?
The higher the current the more energy is transferred to the thermal energy stores of the components and then the surroundings
The heating usually increases the resistance of the components
if the temperature gets too high it can cause components in the circuit to melt which means the circuit will stop working
Energy transfer happens because of?
Collisions between electrons and the iron ions in the lattice
What are advantages of heating and electric current?
For example, toasters contain a coil of while with a really high resistance. When current passes through the coil, it’s temperature increases so much that it glows off infrared radiation. This radiation transfers energy to the bread and cook it.
Ways of reducing unwanted energy transfer through low resistance wise
Fuses
Fuses melt and break the circuit of the current gets too high
if the current gets too hot the fuse will melt and stop the circuit
How to work out energy transferred
E =IxVxt
energy transferred (joule, J) = current (ampere, A) × potential
difference (volt, V) × time (second, s)
