Electricity Flashcards
What are the two different types of electric charge?
Positive and Negative
Like charges will ___ each other.
Repel
Opposite charges will ___ each other.
Attract
What particles are atoms made up of?
Protons
Neutrons
Electrons
What does it mean if an atom is neutral?
Same number of protons and electrons.
Define the electric current.
The electric current is the flow of electrons through a material.
What is an electrical current considered to be?
An electrical current is considered to be the flow of electrons/negative charges.
What is the smallest unit of electric charge?
One electron
What is current defined as?
The rate of flow of electric charge.
(The charge that passes a point in 1 second.)
What is the symbol and unit of Charge?
Symbol - Q
SI Unit - C (Coulomb)
What is the symbol and unit of current?
Symbol - I
SI Unit - A
What is the symbol and unit of time?
Symbol - t
SI Unit - s
What is the formula for calculating charge?
Q = It
—
Q - Charge (Coulombs)
I - Current (A)
t - Time (s)
What does a battery supply?
Direct current
What is a direct current?
A current in which charges move in only one direction.
What does a signal generator supply?
An alternating current.
How do the charges move in an alternating current?
In an alternating current, charges will move one way and then change direction.
What does the “UK mains supply” supply?
An alternating current at 230V with a frequency of 50Hz.
In an alternating current, what does Hz measure?
In an alternating current, Hz measures how many times the current changes direction every second.
What does the SIGNAL GENERATOR trace on an oscilloscope screen of current/time vary in?
The trace from the signal generator varies in AMPLITUDE on an oscilloscope screen.
What does the BATTERY trace on an oscilloscope screen of current/time vary in?
The trace from the battery does not vary on an oscilloscope screen. It remains CONSTANT.
The oscilloscope trace for an alternating current _____
varies in amplitude.
The oscilloscope trace for a direct current ____
remains constant.
From a power supply to an electrical component, what do electric circuits do?
Electric circuits transfer energy from a power supply to an electrical component.
Describe the structure of a series circuit.
In a series circuit, the electrons have only one path to flow through within the circuit.
A break anywhere in the circuit will cause the circuit to stop working.
Describe the structure of a parallel circuit.
In a parallel circuit, there are more than one path for electrons to flow through.
A break in one of the branches of the circuit will NOT affect the rest of the circuit.
All branches must be broken to stop the current.
What are cells and batteries used for?
Cells and batteries are used to supply energy to an electrical circuit.
What is the chemical change in cells and batteries?
The energy change in cells and batteries is CHEMICAL ENERGY to ELECTRICAL ENERGY.
What exists around an electrical charge?
An electric field.
(Magnet has magnetic field, etc)
Define an electrical field.
An electrical field is a place where a charged particle experiences a force.
What concept is responsible for the flow of electrons around an electrical circuit?
The electrical field.
In what direction does the force move across the ELECTRICAL FIELD LINES in a POSITIVE charge?
Away from the positive charge and towards the negative charge
In what direction does the force move across the ELECTRICAL FIELD LINES in a NEGATIVE charge?
Away from the negative charge and towards the positive charge
What are the field lines between two parallel plates called, and what does it mean?
A UNIFORM FIELD.
This means that all of the charged particles in the field will experience the same size of force.
How must a uniform field be drawn?
With STRAIGHT LINES which are an EQUAL DISTANCE apart.
The CLOSER the lines are to one another, the STRONGER the field.
In an electrical circuit, ___ is carried by electrons around the circuit and converted into others forms of ___ by the ____ in the circuit.
Electrical
Energy
Components
What is the “potential” of the electrons at any point in a circuit?
The POTENTIAL is the amount of electrical energy that the electrons carry at any point within the circuit.
What happens to electrical energy as electrons move between two points in a circuit?
The electrical energy is TRANSFERRED into other forms as electrons move between two points in a circuit.
Define “Potential Difference”.
Potential Difference (Voltage) is the energy that is transferred by 1 coulomb of charge.
Therefore, the POTENTIAL DIFFERENCE of the SUPPLY is a MEASURE of the ENERGY given to each COULOMB OF CHARGE in a circuit.
Describe the apperance of a voltmeter. (bc im too lazy to draw it xoxo)
Circle with V in the middle and a line through it.
Describe the apperance of an ammeter. (bc im too lazy to draw it xoxo)
Circle with A in the middle and a line through it.
Describe the apperance of a motor. (bc im too lazy to draw it xoxo)
Circle with M in the middle and a line through it.
Describe the apperance of a fuse. (bc im too lazy to draw it xoxo)
A rectangle with a horizontal line OVER it.
Describe the apperance of a resistor. (bc im too lazy to draw it xoxo)
A rectangle with a horizontal line BENEATH it.
Describe the apperance of a switch. (bc im too lazy to draw it xoxo)
Straight line
Straight line break and tilt up
Straight line continue flat
State three features relating to Current.
- Electrical current is measured in AMPERES (A)
- An AMMETER measures the size of an electrical current.
- An AMMETER is connected in SERIES of a circuit.
State three features relating to Voltage.
- Voltage is measured in Volts (V)
- Voltage is measured ACROSS THE CIRCUIT using a VOLTMETER.
- A voltmeter is connected in parallel.
(Voltage is always measured ACROSS a component)
In a series circuit, the current is ___ at all points.
The same
In a series circuit, how is the voltage of the supply calculated?
By adding up the voltage of all of the components.
In a parallel circuit, how is the total current drawn from the supply calculated?
By adding up the current through each branch.
In a parallel circuit, what is the voltage across each branch equal to when added up?
The supply voltage.
Total current in a series circuit _____
Remains the same.
Total current in a parallel circuit ____
Is calculated by adding currents of branches.
Total voltage in a series circuit _____
Is calculated by adding up the voltage across all of the circuit’s components.
Total voltage in a parallel circuit _____
Remains the same.
____ allow a current to flow through them easily.
Electrical Conductors
___ do not easily allow a current to flow through them.
Electrical Insulators.
Conductors have a ____ resistance to electrical current, whereas insulators have ____
Low resistance
High resistance
Define resistance.
Resistance (R) is the property of a material which defines its opposition to electrical current flowing through it.
What’s the relationship between resistance and current?
The SMALLER the resistance, the LARGER the current.
The LARGER the resistance, the SMALLER the current.
They are inversely proportional.
How is resistance measured?
Using an Ohmmeter.
State the symbol and unit of resistance.
Symbol - R
Unit - Ohm (Ω)
What does an ohmmeter not need to directly measure the resistance of a component?
A battery
Show the formula for calculating the total resistance in a SERIES CIRCUIT.
RT = R1 + R2 + R3
Show the formula for calculating the total resistance in a PARALLEL CIRCUIT.
1/RT = 1/R1 + 1/R2
How is resistance affected when resistors are added in SERIES?
Total resistance increases
How is resistance affected when resistors are added in PARALLEL?
Total resistance DECREASES (weird i know)
In parallel, how can the total resistance be calculated in a circuit with two identical resistors?
Total resistance = 1/2resistance of one resistor
Why does adding resistors in parallel decrease the total resistance?
Adding resistors in parallel decreases the total resistance because it gives the current more paths to flow through, so it is easier for current to move through the circuit.
What formula represents the relationship between the RESISTANCE OF A CONDUCTOR, the VOLTAGE (potential difference) across it, and the CURRENT through it?
V = IR
—
V - Voltage [potential difference] (V)
I - Current (A)
R - Resistance (Ω)
What is the formula for Ohm’s law?
V = IR
What is the resistance of a resistor on a graph equal to?
The GRADIENT of the line.
(ie. Constant gradient = constant resistance)
The steeper the gradient on a best-fit line on a Current/Voltage graph, the ____ the resistance.
Greater
Using the example of a lamp, how will the temperature be affected as the current increase?
After that, how will resistance be affected?
Temperature will increase.
This will then cause the resistance to increase.
As the temperature of a conductor increases, how is resistance affected?
Resistance increases
Define a fuse.
A fuse is a SAFETY DEVICE which melts if the current in the circuit is too high, thus “breaking” the circuit and cutting off the POWER SUPPLY.
What is a fuse used for?
A fuse is used to protect flexes and household wiring from overheating, and prevent damage to electronic devices.
How is a fuse constructed?
A fuse is constructed using a thin metal strip or filament, which is encased in a protective transparent glass or plastic enclosure.
State the 6 most common pre-defined ratings of fuses.
1A
5A
13A
15A
25A
30A
Where is the fuse located on an electrical device’s plug?
Within the LIVE WIRE.
What is the value of a fuse determined by?
The power rating of an appliance.
What do power ratings above 700W require?
A 13A fuse.
What do power ratings below 700W require?
A 3A fuse.
What is modern household wiring protected by?
Circuit breakers
What is a circuit breaker?
A circuit breaker is a type of fuse that can be reset once it has tripped.
How many parts are electronic systems made of?
Three
Name the parts of an electronic system.
Input > Process > Output
What are the two main types of electronic systems?
Analogue
Digital
Describe an analogue output and how it can be identified.
Analogue outputs have CONTINUOUSLY VARYING values.
(On wave form, they’re rounded like valleys)
Describe a digital output and how it can be identified.
Digital outputs can only have two values: on, or off.
(On wave form, they’re squared like a maze)
Input devices will usually change one form of energy into _____
Electrical Energy
(ie. Microphone changes sound energy into electrical energy)
Output devices will usually change _____ into another form of energy.
Electrical Energy
(ie. Loudspeaker changes electrical energy into sound)
What is the energy change of a microphone?
Sound > Electrical
What type of device is a photovoltaic cell?
Input
What is the energy change in a loudspeaker?
Electrical > Sound
What is the energy change of a buzzer?
Electrical > Sound
What type of device is a buzzer?
Output
What is the energy change in a motor?
Electrical > Kinetic
What is the energy change of a solenoid?
Electrical > Kinetic
What is the energy change of a relay switch?
Electrical > Kinetic
What type of device is a lamp?
Output
What is the energy change of a lamp?
Electrical > Light
What type of device is an LED?
Output
What is the energy change of an LED?
Electrical > Light
What is it called when two resistors are in series with each other?
Voltage Divider Circuit
In a voltage divider circuit, what will happen when the resistance of a resistor increases?
The voltage across that resistor will increase.
The voltage across the OTHER resistor will decrease, despite its resistance remaining unchanged.
(Try to) Describe a LIGHT DEPENDENT CIRCUIT.
Voltage Divider Circuit → Transistor Switch → Output Device
- As light intensity decreases, resistance of LDR increases.
- This means voltage across LDR also increases.
- This is the same voltage as across the base and emitter of the NPN transistor.
- When the base-emitter voltage of the transitor rises above 0.7V, the transistor switches on.
- This allows a current to flow through the transistor and also through the LED.
- The LED will be lit.
(Try to) Describe a TEMPERATURE CONTROLLED CIRCUIT.
Voltage Divider Circuit → Transistor Switch → Output Device
- As temperature decreases, resistance of thermistor increases.
- This means voltage across the thermistor also increases.
- This is the same voltage as across the base and emitter of the NPN transistor.
- When the base-emitter voltage of the transitor rises above 0.7V, the transistor switches on.
- This allows a current to flow through the transistor and also through the LED.
- The LED will be lit.
What does it mean when an appliance is more powerful than another?
It means that the appliance uses up energy at a faster rate than the other.
The word “rate” means per second.
What is electrical power?
A measure of the energy transferred electrically by an appliance every second.
It is measured in Watts (W)
What is the formula for power using energy and time?
P = E/t
—
P - Power (W)
E - Energy (J)
t - Time (s)
What is the formula for power using current and voltage?
P = IV
———
P - Power (W)
I - Current (A)
V - Voltage (V)
Define efficiency.
Efficiency is a measure of how good a machine is at carrying out its main energy change. It is normally expressed as a PERCENTAGE.
What is the formula for efficiency?
Efficiency = Power Out/Power In x 100%
What is the smallest unit of electric charge?
The charge on one electron (but this is not used — too small)
What is the charge on an electron?
-1.6 x 10-19 C
What is the unit of charge?
Coulomb (C)
When a ___ particle experiences a force in an electrical field, the particle must ____. This is due to Newton’s Second Law.
Charged
Accelerate
Why do electrons travel at a constant speed in an electrical circuit?
Electrons travel at a constant speed in an electrical circuit because the resistance in the circuit balances the force from the electrical field.
