Electric Circuits Flashcards
what is the purpose of a switch?
to turn a circuit on (closed) or off (open)
how does a lamp work?
an electrical filament heats the filament inside a bulb so that it gives out light
what is a resistor?
it restricts or limits the flow of electrical current. a fixed resistor has a resistance that doesn’t change while a variable resistor’s resistance can be changed by moving a slider on the resistor
what is a thermistor?
it has a resistance that changes based on temperature - the colder it is, the higher the resistance
what is an LDR?
Light Dependent Resistor - resistance changes depending on light intensity - the lower the light intensity, the higher the resistance
what is the purpose of a semiconductor diode?
it allows current to flow in one direction only
what does a voltmeter do?
how do you connect it to a circuit?
- it measures potential difference
- you connect it in parallel (across the component)
what does an ammeter do?
how do you connect it to a circuit?
- it measures current
- you connect it in series (in line with the component)
how do you know if a circuit is complete?
if you can follow a wire from one end of the power supply, through the components, to the other end of the power supply, it is complete
what are the 2 types of current and describe them
- direct current - electrons flows in one direction only
- alternating current - direction of electron flow continually reverses
what is an electron?
it is a negatively charged particle that transfers energy through a wire as electricity
what is charge?
it is a property of certain objects like electrons and protons - they experience a force when in electric fields
how is charge measured?
bonus: how many electrons are in each of these?
- coulombs
- 1 coulomb = 6.25 x 10^18 electrons
what is current?
the rate of flow of electric charge
in what direction does current flow in an electric circuit?
it flows from positive to negative
what is the formula to calculate the amount of charge passing a point in the circuit?
charge = current x time
Q = It
Q = C
I = A
t = s
in a series circuit, current…
…is the same everywhere
how would you describe one amp?
the current that flows when one coulomb of charge passes a point in the circuit in one second
what 2 things does the current flowing through a component depend on?
- resistance of the component
- potential difference across the component
current will only flow through a circuit if there is…
…potential difference
what is potential difference?
it measures the amount of energy transferred per unit of charge
what is the unit of potential difference?
Volts (V)
1 V = ?
1 Joule per Coulomb
what is the formula to calculate potential difference?
potential difference = energy / charge
V = E/Q
V = V
E = J
Q = C
what is resistance?
anything in the circuit which reduces the flow of current
what is resistance measured in?
ohms (Ω)
the larger the resistance…
…the smaller the current
what is the formula linking resistance, potential difference and current?
potential difference = current x resistance
V = IR
V = V
I = A
R = Ω
what are the relative resistances of conductors and insulators?
- conductors = low resistance
- insulators = high resistance
what is an ohmic conductor?
a device that obeys Ohm’s Law like wires or resistors
what is Ohm’s Law?
current and potential difference are directly proportional
as temperature of the filament in a filament bulb increases…
…resistance of the filament increases
why do diodes not let current flow in the opposite direction?
it has a very high resistance in the reverse direction
what are some components that are not ohmic conductors?
how do their resistances change?
- lamps, diodes, thermistors and LDRs
- resistance changes with current flowing through the component
what are the uses of thermistors?
- thermostats - resistance varies with temperature so you can detect temperature of the thermistor and the surroundings - can be used in a car engine to prevent overheating
what are the uses of LDRs?
- automatic night lights/outdoor lights - light levels fall, resistance of the LDR increases which triggers the light to turn on
- burglar detectors - light is shone down. If the burglar steps in front of it and breaks the light beam, resistance of LDR shoots up and triggers an alarm
what are the 2 ways you can set up a circuit?
- in series
- in parallel
how does current flow in a series circuit?
current is the same everywhere
I1 = I2 = I3 …
what would happen if one bulb blew out in a series circuit?
current wouldn’t be able to flow around the circuit - the circuit would be broken
how does pd work in a series circuit?
- energy is transferred from the power supply and is shared all across the circuit
- total pd = sum of all pds across all components
- total V = V1 + V2…
how does resistance work in a series circuit?
- current has to flow through all the resistors so pd is shared across all of them
- total resistance is all the resistances added together
- total R = R1 + R2 …
what happens if a component breaks in a parallel circuit?
not much - only components on that branch would be affected. The other branches are independent of each other
how does current work in parallel circuits?
- current splits as it leaves the cell and goes into one of the loops
- total current is the currents of each branch added together
- total I = I2 + I3 + I4 …
how does pd work in parallel circuits?
- each branch gets the same pd as the source so pd is the same across all components
- total V = V1 + V2 + V3 …
how does resistance work in parallel circuits?
- imagine 2 resistors are connected in parallel
- both resistors have the same pd across them
- but becuase of the extra branch, current has more than one path to go through
- more total current can flow through the circuit
- using V = IR, an increase in current means a decrease in the total resistance of a circuit
is it possible to have components connected in series and in parallel in the same circuit?
yes
which is more commonly used in actual things: parallel circuits or series circuits?
parallel circuits - everything can be turned on and off separately
what is the formula for power in electric circuits?
power = current x potential difference OR power = current^2 x resistance
P = IV or P = I^2R
P = W
I = A
V = V
R = Ω
how is energy transferred in electric circuits?
- as electrons flow through wires, they collide with ions in the wire, causing the ions to vibrate more
- increased ion vibration = increased wire temperature
- energy is transferred: chemical energy store of battery -> internal energy store of wire
1W = ?
1J/s
what 2 ways can electric power be transferred?
- low current with high voltage
- high current with low voltage
what is the most efficient way of transmitting electricity and why?
- at a high voltage with a low current - wires stay cooler
- high current has a higher heating effect on the wires so more energy is lost as heat energy
