Topic 2 - Electricity Flashcards
What is Alternating Potential Difference?
A continually oscillating current flow, which
results in the potential difference across two points continually oscillating between a positive and negative value.
What are are Amps?
The unit that is used for current.
What is attraction?
A force pulling two opposite charges together, when they are brought near each other.
What is a coulomb?
The units that are used for charge.
What is a diode?
A component that only allows current to flow through in the forward
direction. They have very large resistances in the reverse direction.
What is Direct Potential Difference?
A one directional current flow.
What is the earth wire?
The green and yellow striped safety wire that prevents an appliance from becoming live.
What are electric field lines?
Line representing an electrical field, that point in the direction in which a positive charge would experience an electric force.
What is an electric field?
A region in which a charge will experience a non-contact, electric force. All charged objects have an electric field around them, and this field is stronger the closer you are to the charge.
What is an electrical current?
The rate of flow of electrical charge. It’s value is the same at any position in a single closed loop.
What is electrical work?
When charge flows in a circuit, electrical work is said to be done.
What is a filament lamp?
A light emitting component consisting of an enclosed metal filament. Its resistance increases as the filament’s temperature increases.
What is insulation?
The coating around power cables that prevents electrocution and is
colour coded to allow for easy identification.
What is an Light Dependent Resistor (LDR)?
A light sensitive component whose resistance increases as its temperature decreases.
What is a live wire?
The brown coloured wire that carries the alternating current from the supply in a mains power supply.
What is mains electricity?
An ac supply, which in the UK has a frequency of 50Hz a value of 230V
What is a neutral wire?
The blue coloured wire that completes the circuit in a mains power supply.
What is a Non contact force?
A force experienced between two separated objects. Examples include gravity, and magnetic and electric forces.
What is a Ohmic Conductor?
A conductor whose current flow is directly proportional to the potential difference across it, when held at a constant temperature.
What is Ohms?
It is the unit that is used for resistance.
What does parallel mean?
Components connected in parallel have the same potential difference across each component. The total current is equal to the sum of the currents flowing through each component.
What does potential difference mean?
The product of a component’s resistance and the magnitude of current flow through it.
What does repulsion mean?
Caused when two like-charges are brought near each other.
What is resistance?
A measure of the opposition to current flow.
What does the phrase ‘resistors in parallel’ mean?
The total resistance is equal to the inverse of the sum of
the inverses of the resistance of the parallel components. The total resistance of two parallel resistors is always less than the lowest individual resistor value.
What does the phrase ‘resistors in series’ mean?
The total resistance is equal to the sum of the resistances of the individual components.
What does series mean?
Components connected in series have the same current passing through each component but share the total potential difference of the power supply.
What does static charge mean?
The charge caused by an imbalance of positive and negative charges in, or on, an object’s surface. It is often caused by electrons being rubbed from one surface onto another.
What is a step down transformer?
Devices found between the transmission cables and
the consumer that lower the potential difference of the power so it is at safe,
usable levels.
What is a step up transformer?
Devices that increase the potential difference generated by a power station, so that the electrical power transmitted along the transmission cables is at a higher potential.
What is the national grid?
The network of power stations, transformers and cables that connect consumers to power stations.
What is a thermistor?
A temperature dependent component, whose resistance increases
as its temperature decreases.
What is a volt?
It is the unit that is used for potential difference.
What two factors does the current in a circuit depend on?
- Potential Difference (V)
- Resistance (R)
What is an ohmic conductor and state the conditions that are required?
- A conductor for which current and potential difference are directly proportional
- Resistance remains constant as current changes
- Temperature must be constant
List four components for which resistance is not constant as current changes?
- Lamps
- Diodes
- Thermistors
- Light Dependant Resistors
How does the potential difference across two components vary when connected in series and parallel?
- Series: Total P.D is shared between each component
- Parallel: P.D across each component is the same.
If two resistors are connected in parallel, what can be said about their combined total resistance?
Their total resistance is less than the smallest of the two individual resistance.
If two resistors are connected in series, what can be said about their total resistance?
Their total combined resistance is equal to the sum of the two individual resistances.
How should you connect an ammeter in a circuit to measure current?
Ammeters should be connected in series with the component that they are measuring current through.
How should you connect a voltmeter in a circuit to measure potential difference?
Voltmeters should be connected in parallel to the component that they are measuring the potential difference of.
Define alternating current and direct current?
- Alternating current: Current that continuously changes direction at a specific frequency
- Direct current: One directional current flow
What two main factors does amount of energy transferred by an appliance depend on?
- How long the appliance is being used for
- The power of the appliance
Why do transmission lines transfer electricity at high potentials?
- A high potential, results in a low current
- The lower the current, the less energy that is wasted as heat
- Therefore it is more efficient
Why does the potential need to be decreased between transmission lines and houses?
- Lower potentials are safer for domestic use and reduces the likelihood of severe electrocution
- Appliances are designed for 230V
Why can insulators become electrically charged when rubbed together?
- Electrons are rubbed from one material onto the other
- The material gaining electrons becomes negatively charged
- The material losing electrons becomes equally positively charged
In situations where sparks are unwanted, what precaution must be taken to prevent the build up of static charge?
Any surfaces that are rubbing against each other should be earthed to allow the charge to flow off the material.
