Topic 2 Flashcards by nura souliman

What is current?

The flow of electrical charge

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When does electrical charge flow?

electrical charge will only flow round a complete (closed) circuit when there is a potential difference (voltage)

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What is the unit of current?

ampere, A

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What is potential difference (voltage)?

the driving force that pushes the charge around

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What is the unit of potential difference (voltage)?

volts, V

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What is resistance?

anything that slows the flow down

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What is the unit of resistance?

ohm (horse shoe)

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What does the current flowing through a component depend on?

the potential difference across it and the resistance of the component

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What does a greater resistance across the component cause?

The greater the resistance across the components ,the smaller the current that flows

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What do ohmic conductors have?

constant resistance

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What happens to the resistance of some components as current changes?

For some components, as the current flowing through them is changed the resistance of the component changes as well.

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What does the resistance depend on in diodes?

the direction of the current. They will happily let current flow in one direction, but have a very high resistance if it is reversed.

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What happens when a electrical charge flows through a filament lamp?

It transfers some energy to the thermal energy store of the filament, which is designed to heat up. Resistance increases with temperature, so as the current increases, the filament lamp heats up more and the resistance increases

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What is LDR short for?

Light dependent resistor

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What is an LDR?

a resistor that is dependent on the intensity of light

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What happens to the LDR as it gets lighter and darker?

In bright light the resistance falls
In darkness the resistance is at its highest

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What is a thermistor?

A temperature dependent resistor

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What happens to the resistance of a thermistor in hot and cool conditions?

In hot conditions the resistance drops and in cool conditions the resistance goes up.

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In what type of circuit can you use LDRs and Thermistors in?

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sensing circuit

What can sensing circuits be used for?

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to turn on or increase the power to components depending on the conditions that they are in.

What does adding a resistor to a parallel circuit do to the resistance of the circuit?

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Adding a resistor to a parallel circuit reduces the total resistance

What are the types of electricity supplies?

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alternating current (ac) and direct current (dc)

Describe the current in an alternating current supply.

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In an alternating current supply the current is constantly changing directions. Alternating currents are produced by alternating voltages in which the positive and negative ends keep alternating.

What is the frequency of an alternating currents main supply?

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50 cycles per second or 50 Hz

What type of current do cells and batteries supply?

direct current

What is a direct current and what is it created by?

Direct current is a current that is always flowing in the same direction. It's created by direct voltage.

What colour is a neutral wire?

blue

What is the role of the neutral wire?

carries away current -electricity normally flows in through the live wire and out through the neutral wire. It is around 0 V.

What colour is a live wire?

brown

What does the live wire provide?

The live wire provides the alternating potential difference (at about 230V) from the main supply.

What colour is a earth wire?

green and yellow

What is the role of the earth wire?

It is for protecting the wiring and for safety - it stops the appliance casing from becoming live. It doesn't usually carry a current - only when there is a fault. Its also a 0 V.

What wire can give you an electric shock and why?

The live wire. Your body is at 0 V . This means that if you touch the live wire a large potential difference is produced across your body and a current flows through you. This causes a large electric shock that could injure or kill you.

What is potential difference?

Energy transferred per charge passed

How do we know that energy has been transferred?

When an electrical charge goes through a change in potential difference

What is the national grid?

The national grid is a giant system of cables and transformers that cover the UK and connect power stations to consumers.

How is electricity distributed?

via the national grid

What does the national grid do?

The national grid transfers electrical power from power stations anywhere on the grid (the supply) to anywhere else on the grid where it's needed (the demand - e.g. homes)

What does the national grid need to transfer huge amounts of power?

they need either a high potential difference or a high current

What is the problem with the national grid using a high current?

The problem with a high current is that you loose a lot of energy as the wires heat up and energy is transferred to the thermal energy store of the surroundings

What do the national grid use in terms of potential difference and is this efficient?

The national grid uses a high potential difference and a low current. Its much cheaper to boost the potential difference up really high and keep the current as low as possible. For a given power, increasing the potential difference decreases the current, which decreases the energy lost by heating the wires and the surroundings. This makes the national grid an efficient way to transfer energy.

What is a build up of static electricity caused by?

friction

How does friction cause static electricity?

When certain insulating materials are rubbed together, negatively charged electrons will be scraped off one and dumped on the other. This will leave the materials electrically charged, with a positive static charge on one and an equal negative charge on the other

What is a positive static charge caused by?

A positive static charge is caused by electrons moving away elsewhere. The materials that loses the electrons loses some negative charge, and is left with an equal positive charge. THE POSITIVE CHRGES DON'T MOVE.

What can too much static cause?

sparks

How can too much static cause sparks?

As electric charge builds on an object, the potential difference between the object and the earth increases. If the potential difference gets large enough, electrons can jump across the gap between the charge object and the earth - this is the spark.

What do electric charges create?

An electric field. The closer you get to the object, the stronger the field is

Topic 2 Flashcards

(47 cards)