P4 - Electric Circits Flashcards
What is an electric current?
- An electric current is a flow of charge.
- Most electric currents use a flow of electrons (negatively charged).
- Current is measured in amps (A).
What is a circit diagram?
- A circuit diagram shows how the components in an electrical circuit are connected.
- Each component has its own symbol.
- When drawing a circit diagram use straight, clear lines.
What do cells and batteries do in an electrical circit? (Components)
Provide the ‘push’ for electrons in a circit.
What does an ammeter do in an electrical circit? (Component)
Used to measure current.
What does a voltmeter do in an electrical circit? (Component)
Used to measure the potencial difference (voltage).
What does a lamp do in an electrical circit? (Component)
Ouputs light when current flows through it.
What does a resistor do in an electrical circit? (Component)
Limits the current in a circit
What is an LDR? (Component)
Light dependent resistor
What does a fuse do in an electrical circit? (Component)
Melts and breaks the circit if the current is too high.
What does an LED do in an electrical circit? (Component)
Emitts light when current passes through it
What does a switch do in an electrical circit? (Component)
Enables current in a circit to be switched on or off.
What does a thermsistor do in an electrical circit? (Component)
Temperature dependent resistor.
What does a variable resistor do in an electrical circit? (Component)
Allows current to be varied.
What is the unit for charge
Coulombs (C)
What is the charge of an electron
-1 atomic charge
or
-1.6x10^-19 Coulombs
What does a motor do in an electrical circit? (Component)
Turns electrical energy into kinetic energy
What does a diode do in an electrical circit? (Component)
Diodes only let electricity go one direction in the circit
Write an equation that connects charge, current and time.
Q = I x t
Q is Charge (Coulombs)
I is Current (Amps)
t is time (seconds)
Conventional current flows from _________ to _______.
positive, negative
Electron flow is from the _______ terminal of the cell to the _______ terminal of the cell.
negative, positive
Electron flow is _________ to convencional current direction.
opposite
DO NOT GET MIXED UP
What is potential difference (also known as voltage)?
Potential difference is the amount of work done (energy transferred) by each coulomb of charge that passes through the circuit between two points.
Write an equation connecting potential difference, charge and energy.
Potential difference (V) = Energy (J) / Charge (C)
V = E/Q
What are some different equations for electrical energy?
Energy(J) = Power(W) x time(s)
Energy(J) = Charge(C) x Potential difference(V)
Energy(J) = Current(A) x time(s) x Potential difference(V)
Name a metal that is a better conductor than copper.
Gold is a better conductor than copper.
But due to how expensive it is, its mostly used in smaller appliances like inside a phone.
How does current and voltage behave in a series circuit?
- The current stays the same throughout the circuit
- The voltage is split across each component (e.g bulbs)
How does current and voltage behave in a parallel circuit?
- The current is split between each of the components (e.g bulbs)
- The voltage stays the same throughout the circut
What is resistance?
- Electrical resistance in a circuit is the opposition to the flow of charge
- Resistance is measured in a unit called Ohms (Ω)
How does resistance work?
- Electricity is the flow of electrons along a wire. As the electrons move along the wire they collide with the metal ions in the wire.
- These collisions are what causes resistance
What happens in metals with a high resistance when they conduct electricity?
- In metals with a high resistance, more collisions occur and electrical energy is wasted as light and heat.
- The current decreases and the metal gets hotter.
How do filament bulbs turn electrical energy into light?
- Filament bulbs use a thin wire with a high resistance.
- This causes the electrons to collide more with the metal atoms.
- This turns the electrical energy into heat and light energy.
Electrical energy will always flow in the path with the ___________.
least resistance
What is a resistor?
A resistor is a component designed to reduce the current.
- A variable resistor has a resistance that can be changed.
- A fixed resistor has a resistance that remains the same.
How do kettles transfer electrical energy into heat energy to boil water?
The heating element in this kettle is a coil of metal that resists electricity.
- As current is passed through the metal,
resistance causes the metal to get hot and so boils the water.
What factors affect the resistance of the wire
- How thin it is - thinner wires increase resistance.
- How hot it is - a hotter wire increases resistance.
- the length of the wire - longer wires have a higher resistance.
- The material used - the reactivity of a material is always the same.
What is Ohm’s law?
The current through a resistor at a constant temperature is directly proportional to the potential difference across the resistor.
Write Ohm’s law as an equation.
Potential difference(V) = Current(A) x Resistance(Ω)
V=IxR
In a _______ circuit the total resistance in the circuit is the the resistance of the all the resistors added up.
series
Categoric data is usually displayed using a…
… bar chart.
Continuous data is usually displayed using a…
… line graph
A current-voltage graph the line of best fit will always pass through the…
origin (0,0).
(As long as the temperature remains constant while collecting data)
The gradient of a current-voltage graph is equal to…
… 1/resistance.
In a current-voltage graph a line of best fit with a steeper gradient means that the material has a ______ resistance.
lower
Why does a filament lamp not follow Ohm’s law?
Its resistance increases as the temperature of its filament increases. So the current flowing through a filament lamp is not directly proportional to the voltage across it.
The diode has a very high resistance in ____________. This means that current can only flow in the ____________.
one direction
other direction
What are diodes used for and why?
Diodes are electronic components that can be used to regulate the voltage in circuits and to make logic gates.
Light-emitting diodes (LEDs) give off light and are often used for indicator lights in electrical equipment such as computers and television sets.
Memorise the voltage current graphs for the following components…
Resistor
Filament lamp
Diode
How is the total resistance of a circuit calculated in a series circuit?
RT = R1 + R2 + R3
Adding components in series increases the total resistance in a circuit.
How is the total resistance of a circuit calculated in a parallel circuit?
1/RT = 1/R1 + 1/R2 + 1/R3
