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)
What is power?
The energy transferred per second and it’s measured in watts (W)
What’s the power rating? Tell us
Tells you the maximum amount of energy transferred between stores per second when the appliance is in use
Microwaves have a range of power ratings. A microwave with a power rating of 500 W will take longer to cook food than one with a power rating of 750 W.
What is the equation for power?
P = E divided by t
power (watt, W) = energy transferred (joule, J) ÷ time taken
(second, s)
How does power transfer in any circuit device relate to the potential difference across it in the current isn’t it?
The power transferred by an appliance depends on the potential difference across it and the current flowing through it
the potential difference tells you how much energy each unit of charge transfers and the current tells you how much charge pass it per unit time so both will affect the rate that energy is transferred to an appliance and that the rate at which transfers energy to other stores
What are the two equations for electrical power?
P = IxV
electrical power (watt, W) = current (ampere, A) × potential
difference (volt, V)
electrical power (watt, W) = current squared (ampere2, A2) ×
resistance (ohm, Ω)
P = I squared x R
What is the difference between direct and alternating voltage?
Cells and battery supply direct current
In the direct current the charges always move in the same direction
Direct current is created by direct voltage ( a potential difference that is only positive or negative)
An alternating current supplies, the charges are constantly changing direction
Alternating currents are produced by alternating voltages
The UK main supply is in alternating current supply at around 230 V
The frequency of the alternating current main supply is 50 cps or 50 Hz
How is energy transferred in different domestic devices
From batteries and the alternating current mains to the energy of the motors and heating devices
What is direct current
- d.c.
- movement of charge in one direction only and recall that cells and batteries supply direct current
What is alternating current
- a.c.
- movement of charge changes direction
What is the difference in function between live and neutral mains input wires
LIVE
- brown colour
- live wire carries the voltage
- alternates between a high +ve and -ve voltage of about 230V
NEUTRAL
- blue
- neutral wire completes the circuit - when the appliance is working normally, current flows through the live and neutral wires
- it is around 0V
What is the function of the earth wire
- Green and yellow
- it’s for safety and protection of wiring
- carries the current away if something goes wrong and stops the appliance casing going live
What are roles of fuses
A certain incurrent melts diffuse when the amount of current is greater than the fuse rating. Fuses are connected to the live wire, so that breaking the fuse breaks the circuit and cuts off the live supply.
This isolated a whole appliance, making it impossible to get an electric shock from the case. It also prevents the risk of fire caused by the heating effect of a large current.
What is the potential difference between the live wire and the neutral wire?
Equals the supply potential difference, which is 230 V for the mains
What is the potential difference between the live wire and the Earth wire?
230 V
What is the potential difference between the neutral wire and the Earth wire?
0 V
How do circuit breakers work
Circuit breakers turn off quicker than the time taken for a fuse to melt
They can be reset, which is much easier than having to replace the fuse
However, they’re more expensive than fuses
What is the danger of providing any connection between the live and earth?
Human bodies are at 0 V. This means that if you touch the live wire, a large potential difference is produced across your body and the current flows through you. This causes a large electric shock which could injure or even kill you
What does double insulation make appliance safer?
It reduces the danger of an electric shock
If the appliance has a plastic casing and no metal parts are showing then it said to be double insulated, anything with double insulation like that doesn’t need an earth wire – just a life in a neutral wire
