Electricity Flashcards
Which particles are in the nucleus of the atom?
Protons and neutrons
What happens if two positive charges are brought together?
They repel each other
What happens if two negative charges are brought together?
They repel each other
What happens if a positive and a negative charge are brought together?
They attract each other
What is electric charge?
An electric charge occurs when there are fewer or more electrons than protons.
Name one place that electrostatics can be used.
Laser printers
Paints spraying
Cling film
Forensic science
Dust removal
Electrostatic precipitators
Electrostatic separators
What does an electric field line show?
The direction a positive charge would move in that field.
Explain how electrostatics can be used in paint spraying a car.
Car is connected to a negative terminal so that it is negatively charged.
Spray gun is made positively charged so the paint particles are positive.
The poistive paint is attracted to the negative car.
Areas of the car already covered in paint will repel any more charged paint.
What is the effect of an electric field on a charge?
The charge will experience a force.
What would the field lines around a positive point charge look like?
Field lines show direction away from the positive point charge.
What would the field lines around a negative point charge look like?
Field lines show direction towards the negative point charge
What would the field lines look between parallel plates?
Field lines run from positive to negative plate, with a bulge at the ends of the parallel plate.
How can you indicate a stronger electric field?
More field lines
How can you indicate a weaker electric field?
Fewer field lines
How is a uniform electric field represented?
Evenly spaced field lines
What would happen to an electron being fired through the electric field below?
It would experience a force and be attracted to the positive plate
What is current?
The charge transferred per second
What is d.c.?
Direct current. Charges move in one direction only.
What is a.c.?
Alternating current. The charges change direction constantly
Name one source of d.c.
A battery
How can you tell from this oscilloscope image that this is a.c.?
(its wavey)
The trace shows a change in direction
Name one source of a.c.
Mains supply
What type of current is represented by this oscilloscope image?
(its a straight line)
d.c.
What type of current is represented by this oscilloscope image?
(its wavey)
a.c.
What is meant by the potential difference (voltage) of a supply?
It is the number of Joules of energy given to each coulomb of charge passing through the cell
Which device measures current?
Ammeter
Which device measures voltage?
Voltmeter
Which devi measures resistance?
Ohmmeter
What is the symbol for a voltmeter?
A circle with a V in it
How should an ammeter be connected to measure the current in a component?
In series
How should a voltmeter be connected to measure the voltage across a component?
In parellel
How can you identify a series circuit?
It is a circuit with only one path round it
What is the symbol for an Ohmmeter?
Circle with an Omega in it
What is the symbol for an ammeter?
A circle with an A in it
How can a parallel circuit be identified?
It is a circuit with more than one path round it.
What is the rule for voltages in a series circuit?
The voltage across each component added together is equal to the supply voltage.
What happens if you unscrew one of the lamps in the circuit below? Why?
The other lamps go out. There is a break in the circuit and the current does not have a complete route to the battery.
If you heat a conductor, what happens to it’s resistance?
It increases
What is the rule for current in a series circuit?
The current is the same everywhere
What is the function of a transistor?
Electronic switch
What is the rule for volatges in a parallel circuit?
The voltage across each branch is equal to the supply voltage.
What is the rule for current in a parallel circuit?
The supply current is equal to the current in each branch added together.
What is the energy change in a loudspeaker?
Electrical to sound
What is the function of a MOSFET?
Electronic switch
What is the energy change in a battery?
Chemical to electrical
What is the energy change in a bulb?
Electrical to light (+heat)
What is the energy change in a motor?
Electrical to kinetic
What is the energy change in a buzzer?
Electrical to sound
What is the energy change in a photovoltaic cell?
Light to electrical
What is the energy change in a LED?
Electrical to light
State a device that can be used in a temperature sensor
Thermistor
What is a thermistor?
A resistor whose resistance changes with changes in temperature
What is the energy change in a microphone?
Sound to electrical
State two places a variable resistor can be used.
Light dimmer switch
Speed control on Scalextric cars
Volume control on a radio
What is a Light Dependent Resistor?
A resistor whose resistance changes with changes in light level
What is a fuse?
A safety device that protects the circuit from surges in current
State a device that can be used in a light sensor
LDR
What happens if you increase the resistance in a circuit?
The current will decrease
How should a diode or LED be connected with a battery to light correctly?
Small line on battery points to small line on LED or diode.
Explain how a fuse works.
A fuse is a thin wire. If too much current passes through it, it will get hot and melt. This breaks the circuit.
Why is an LED normally connected in series with a resistor?
Resistor is to protect the LED by limiting the current in the LED.
What does a capacitor do?
Stores charge or energy
What will be the voltage across a capacitor when it is fully charged?
The supply voltage
What will be the voltage across a capacitor when it is fully discharged?
Zero volts
What is meant by capacitance?
Charge stored per unit volt
What is power?
The energy used per second
What two factors effect the running cost of an appliance?
The time it is used for
The power rating of the appliance
What is the rule for selecting a fuse from a power rating?
Appliances less than 720W use a 3A fuse Appliances more than 720W use a 13A fuse
What is the charge on a neutron?
No charge
What is the charge on a proton?
Positive
How can power losses be reduced in transmission lines?
By increasing the transmission voltage and so decreasing the transmission current.
Power loss P = I2R, so if the current is reduced the power lost is reduced.
What is the stated value of the mains?
230V, 50Hz
What is the charge on an electron?
Negative
When would you use a relay?
To switch on a high current circuit using a low current circuit for safety.
How does a relay work?
Close a switch to make a current flow in a wire.
This creates an electromagnet.
Electromagnet attracts metal switch.
This completes the second circuit and the lamp switches on.
What is the energy change in a buzzer?
Electrical to sound
What is direct current
a one-direction flow of current. Cells and batteries in circuits provide direct current.
What is the voltage of the UK mains supply
230V
The equation for Charge and current
Q = I x t
Q = Charge in Coulombs (C)
I = Current in Amperes (A)
t = Time in seconds (s)
What is alternating current
a current that changes direction continuously over time. The UK mains supply is an example of alternating current.
What is Ohms law
the relationship between Current, Resistance and Voltage. In other words, “The current through a conductor between two points is directly proportional to the voltage across two points.”
The equation for voltage
Voltage = Current x Resistance.
How do calculate resistance in a series circuit
Adding the resistance of each component together to get the total.
Total resistance = R1 + R2 + R3
How do you calculate resistance in a parallel circuit
1/Total resistance = 1/R1 + 1/R2 +1/R3
How can resistance be affected by length of wire and temperature
When temperature increases, resistance increases. As length of wire increases, resistance increases.
What is a voltage divider
a simple circuit where two resistors are connected in series, which divide a supply voltage.
What is the equation used to calculate an unknown value of voltage or resistance in a voltage divider
V1/V2=R1/R2
Vs=V1+V2
V1=Vs x R1/R1+R2
What is electrical power
the energy transferred in a period of time in a circuit
How do you calculate electrical power
Power = Energy/time
Power is measured in Watts (W)
Energy is measured in Joules (J)
Time is measured in seconds (s)
What is voltage measured in
Voltage (V) is measured in Volts
What is power measured in
Power (P) is measured in Watts
What is Current measured in
Current (I) is measured in Amperes
What is resistance measured on
Resistance is measured in Ohms
What are the three equations for power
Power = Current x Voltage
Power = Current^2 x Resistance
Power = Voltage ^2 / Resistance
What do fuses do for a circuit
Fuses protect a circuit when current gets too high.
For appliances that have power up to 720W what Amp fuse should you use
A 3 Amp fuse
For appliances that have power over 720W what Amp fuse should you use
13 Amp fuse
What is a series circuit
A series circuit is one where the current follows in one path through every component of the circuit.
How is voltage handled in a series circuit
Voltage is divided between the components in a series circuit
