Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
53 Cards in this Set
- Front
- Back
|
What is current measured in?
|
Amps (A)
|
|
|
What is the symbol for current in equations?
|
An italic capital I (with line on top and bottom!).
|
|
|
What instrument measures current?
|
An ammeter
|
|
|
Does current flow across or through a component?
|
Through!
|
|
|
How is an ammeter fitted into a circuit?
|
It is placed in series with whatever component you wish to measure the current in.
|
|
|
What does the size of the current in a circuit depend on?
|
How hard the supply tries to push charge through the circuit and how hard the circuit resists having charge pushed through it
|
|
|
What 'pushes' the current through the circuit?
|
The potential difference (voltage) provided by the power supply (battery or lab pack).
|
|
|
What resists the charge movement?
|
The resistance of the component.
|
|
|
What is resistance measured in?
|
Ohms
|
|
|
What measures p.d. ?
|
A voltmeter
|
|
|
How is a voltmeter fitted in the circuit?
|
It is connected in parallel with the component across which it is measuring the voltage drop (potential drop or potential difference).
|
|
|
What is resistance?
|
The ratio of potential difference across a component to the current flowing through it.
|
|
|
How can you find the resistance of a component?
|
By measuring the current through it with an ammeter; and the potential difference of the component with a voltmeter and then dividing the p.d. by the current.
|
|
|
What are current-potential difference graphs called?
|
Characteristic curves.
|
|
|
What are characteristic curves used for?
|
They are a visual way of seeing how a component will behave if you put different potential differences across it.
|
|
|
What is Ohm's Law?
|
The current through a resistor (at a constant temperature) is directly proportional to the potential difference across the resistor.
|
|
|
Why is the characteristic curve of the filament lamp curved?
|
The resistance of a filament lamp increases as the temperature of the filament increases.
|
|
|
Why is the graph for a resistor a straight line through the origin?
|
Because the resistor has a constant resistance.
|
|
|
Why does the characteristic of the diode have virtually no current in reverse bias?
|
The diode has a very high resistance when connected in reverse bias.
|
|
|
What kind of resistance does a diode have when connected in forward bias?
|
Very low resistance if a voltage of more than 0.6V is connected across it.
|
|
|
Describe how the resistance of a light-dependent resistor (LDR) changes as light intensity increases.
|
It decreases (Lighter conditions - Lower resistance)
|
|
|
Describe how the resistance of a thermistor changes as the temperature increases.
|
It decreases.
|
|
|
How do you work out the potential difference provided by cells connected in series?
|
It is the sum of the potential difference of each cell (depending on the direction in which they are connected - see Cyberphysics graphic).
|
|
|
For components connected in series how do you calculate the total resistance?
|
The total resistance is the sum of the resistance of each component.
|
|
|
For components connected in series what do you know about the current through each component?
|
It is the same.
|
|
|
For components connected in series what do you know about the total potential difference?
|
The potential difference of the supply is shared between the components according to their resistance - bigger resistance - bigger share.
|
|
|
For components connected in parallel what do you know about the potential difference across each component?
|
It is the same.
|
|
|
For components connected in parallel what do you know about the current through them?
|
The total current through the whole circuit is the sum of the currents through the separate components - and the lower the resistance of the component the more current flows.
|
|
|
What is d.c.?
|
Direct current - current that always flows in the same direction.
|
|
|
What is a.c.?
|
Alternating current - current that is constantly changing direction.
|
|
|
What type of current do cells and batteries supply?
|
d.c.
|
|
|
What is mains electricity?
|
It is an a.c. supply that is supplied via the sockets in our houses.
|
|
|
What is mains frequency in the UK?
|
50 cycles per second (50 hertz or 50Hz).
|
|
|
What is UK mains supply voltage?
|
230 volts.
|
|
|
How are most electrical appliances are connected to the mains?
|
Using a cable and a three-pin plug.
|
|
|
What is the structure of electrical cable?
|
Three insulated strands (brown, blue and green/yellow stripe) within an insulating sheath
|
|
|
What is the right hand pin of a three-pin plug and what colour wire is connected to it?
|
Live - brown wire.
|
|
|
What is the left hand pin of a three-pin plug and what colour wire is connected to it?
|
Neutral - blue wire.
|
|
|
What is the top pin of a three-pin plug and what colour wire is connected to it?
|
Live - yellow/green wire.
|
|
|
Which pin is connected to the fuse?
|
The live pin.
|
|
|
What is the purpose of a fuse?
|
If an electrical fault causes too great a current the circuit should be switched off by a fuse blowing or a circuit breaker.
|
|
|
When the current in a fuse wire exceeds the rating of the fuse, what happens?
|
It will melt (because high current makes wires hot), breaking the circuit.
|
|
|
What should be done to appliances with metal cases?
|
They are usually earthed.
|
|
|
What protects the appliance?
|
The earth wire and fuse together protect the appliance.
|
|
|
What is the voltage of the live terminal?
|
The live terminal of the mains supply alternates between positive and negative potential with respect to the neutral terminal.
|
|
|
What is the voltage of the neutral terminal?
|
It stays at a potential close to zero with respect to earth.
|
|
|
What do electrical appliances do?
|
They transform energy from electrical energy into the type we need.
|
|
|
What does the power of an electrical appliance tell you?
|
It tells you how fast it transforms energy.
|
|
|
What information is stamped onto electrical appliances?
|
Most appliances have their power and the potential difference of the supply they need printed on them.
|
|
|
How do we know what value of fuse to put in an appliance's plug?
|
From the power and voltage we can calculate the current and the fuse it needs.
|
|
|
What is electric current?
|
It is the rate of flow of charge.
|
|
|
What happens when an electrical charge flows through a resistor?
|
Electrical energy is transformed into heat energy (it gets hot).
|
|
|
What is the rate at which energy is transformed in a device?
|
It is called the power - measured in watts (W).
|
