P4 Electric Circuits Flashcards
What is current?
The rate of flow of charge
What is current measured in?
Amps
What the equation for current?
Current = Charge / Time
What is charge measured in?
Coulombs (C)
What is voltage?
The amount of energy transferred for one coulomb of charge
How do you calculate voltage?
Voltage = Energy / Charge
What does resistance do?
It slows down the flow of electrical charges in a ciruit.
What is resistance measured in?
Ohms (Ω)
What are factors which increase resistance?
- Length of the wire
- Higher temperature
What factors decrease resistance?
- Type of material (copper has less resistance)
- Diameter (greater diameter has less resistance)
What is Ohms’ Law?
When the temperature is constant, voltage and current are directly proportional.
This means the resistance is a constant.
What are Ohmic Conductors?
Conductors which follow Ohms Law.
What happens when an insulating material loses an electrons?
It becomes positively charged.
What happens when an insulating material gains electrons?
It becomes negatively charged.
What type of force is between two charged objects?
Non-Contact Force
How do you calculate potential difference across a component?
Potential difference = Energy transferred / Charge
How do you calculate resitance?
Resistance = potential difference / current
In a Filament Lamp as resistance increases …..
temperature increases
A thermistor’s resitance decreases ……
if temperature increases
An LDR’s resistance decreases ….
if the light intensity increases.
How do you calculate resistance using a Filament Lamp graph?
Resistance = 1 / gradient
What makes a filament lamp have a high resistance?
- Thin filament with a small diameter
- Some energy is transfered into thermal energy, so cations vibrate more
What is the function of a diode?
Diodes let current flow through in only one direction because it has a very high resistance in the opposite direction.
When voltage in a diode reaches a certain value…..
current starts to increase
What stays the same in each component of a series circuit?
Current
What is shared between the components of a series circuit?
Total potential difference
When more bulbs are added to a series circuit, why do become dimmer?
Voltage across each bulb decreases and the total resistance of the circuit increases.
What is shared between the components of a parallel circuit?
Current (but not the same amounts)
What is equally shared amongst the components of a parallel circuit?
Potential Difference
Why does adding more resistors in a parallel circuit decreases resistance?
The total current through the resistors is increased and the potential difference across them is unchanged
What does a cell do?
Pushes electrons around a complete circuit
What does a switch do?
It enables you to break and complete a circuit (turn on and off a circuit)
What does a bulb do?
Emits light when current flows through it.
What does a fixed resistor do?
Limits the current in a circuit.
What does a variable resistor do?
It allows the current in a circuit to be varied.
What does the thermistor do?
Allows the current depending on the temperature.
What does a fuse do?
It is designed to melt or break if the current is too great.
What does a diode do?
Allows current through only one direction
What does a light emitting diode (LED) do?
Emits light when a current passed through it
What does a light dependent resistor (LDR) do?
Decreases in resistance as light intensity increases
What does an ammeter do?
It is used to measure electric current (Amps)
What does a voltmeter do?
It is used to measure electric potential difference (Voltage)
Define electrical current.
The flow of electrical charge.
What is potential difference?
Potential difference is the driving force that causes electric charges to flow around a circuit.
- measured in Volts (V)
REQUIRED PRACTICAL - how do you investigate factors affecting resistance of electrical circuits?
1) Using the ruler, measure the distance between the two crocodile clips. This is the “wire length”.
2) Close the switch and record the current and the potential difference
3) Move the claw clips so that the wire length is bigger or smaller. Repeat the measurements of length, current and potential difference.
4) Repeat the experiment for a number of different wire lengths.
