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Physics > [custom] 4.2 test remade > Flashcards

[custom] 4.2 test remade Flashcards

1
Q

Define potential difference.

A

The energy transferred from electrical energy to other forms, per unit charge by the charges passing through the component. It is measured across a component.

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2
Q

Define 1 Volt

A

The PD between two points when 1 Joule of work is done to move a charge of 1 Coulomb.

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3
Q

What equation is used to find Potential Difference and EMF?

A 
V = W/Q
E = W/Q
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4
Q

Potential difference is a measure of what?

A

The work done by charge carriers, which lose energy as they pass through the components in a circuit.

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5
Q

Define electromotive force.

A

The energy transferred from chemical energy into electrical energy per unit charge, by charges passing through a supply.

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6
Q

What is EMF used as a measure for?

A

Used to measure the work done to charge carriers, when they gain energy as they pass through a cell or a power supply.

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7
Q

Explain what resistance is?

A

A measure of how difficult it is for current to flow through a component.

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8
Q

How do we determine the resistance of a component?

What is the resistance equal to on the graph of results?

A

Setup a circuit with a variable power supply, an ammeter in series with the component, and a voltmeter in parallel with the component.

By varying the power supply, we can vary the potential difference across the component, and record the PD and current to calculate the resistance.

The resistance is equal to 1 over the gradient of the IV graph.

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9
Q

State Ohm’s law

A

For a metallic conductor kept at a constant temperature, the current in the wire is directly proportional to the potential difference across it.

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10
Q

Where Ohm’s law is true, components are considered ____, and their IV characteristics graph will have a _____ ______ gradient.

A

Where Ohm’s law is true, components are considered OHMIC, and their IV characteristics graph will have a CONSTANT LINEAR gradient.

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11
Q

What happens when the current across a non ohmic component increases?

A

The metal ions are heated, gaining kinetic energy and vibrate more around their fixed points in the metallic lattice.

This increases the frequency of collisions with electrons, so more work is done on the charge carriers, increasing the resistance.

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12
Q

How are fixed resistors designed?

A

Designed so that their resistance is always constant, despite environmental changes.

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13
Q

Do fixed resistors follow Ohm’s law? Why?

A

They follow Ohm’s law. This is because the PD is proportional to current.

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14
Q

Judging by its IV characteristics, are filament lamps ohmic or non-ohmic?

A

They show that the component is non-ohmic.

but as the magnitude of the current increases,

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15
Q

What are diodes?

A

Components made from semiconductors, which allow current to flow only in one direction.

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16
Q

Are diodes Ohmic or Non-Ohmic?

A

Non Ohmic.

17
Q

What occurs when a diode is reverse biased?

A

It does not conduct at all, and the resistance across it is infinite.

18
Q

What does it mean if a semi-conductor has a negative temp coefficient?

Where would these NTC semi conductors be useful?

A

As the temp of the material increases, the resistance of the material decreases.

They are useful in temp sensing circuits such as thermometers and thermostats.

19
Q

Are thermistors ohmic or non ohmic?

Why?

A

Non ohmic

It is made of an NTC semi conductor material.

20
Q

What are thermistors made of?

What happens as the current through a thermistor increases?

A

It is made of an NTC semi conductor material.

As the current, hence the temperature, through the thermistor increases, the resistance decreases.

21
Q

What are LDRs?

What do they do?

A

LDRs are small, non-ohmic components made from semi conductors.

When the light intensity incident on the resistor increases, the resistance of the LDR decreases.

22
Q

What is resistivity?

A

A measure of how difficult it is for charge to travel through a material.

23
Q

What is resistance proportional to?

A

Proportional to: Length.

Proportional to: 1 / Area
This means it is inversely proportional to area.

24
Q

The resistivity, p, of a material is a ______ property of the material.

It is the same for any ___ of a given material at a set ____.

A

The resistivity, ρ, of a material is a PHYSICAL property of the material.

It is the same for any SHAPE of a given material at a set TEMPERATURE.

25
Q

What is the formula for resistivity?

A

p = RA/L

26
Q

How does the resistivity of a metal vary with temperature?

A

As the temperature increases, the fixed metal ions will vibrate at greater frequency and amplitude.

This increases the number of collisions of electrons with the ions, increasing the resistance.

27
Q

How does the resistivity of a semiconductor vary with temperature?

A

The number density of charge carriers increases with increasing temperature, so the resistance of the material decreases.

28
Q

What is electrical power defined as?

What is it measured in?

A

The rate of energy transfer.

It is measured in watts or Js-1

29
Q

What is a kilowatt-hour defined as?

A

The energy transferred by a device with a power of 1 kilowatt when operated for 1 hour.

30
Q

How is the cost of energy usually given?

A

It is usually given per kilowatt hour (kWh). It can be used to figure out the total cost of running a device.

31
Q

How can power be calculated?

What is it measured in?

A

It can be calculated as the product of the current and the PD between two points. It is measured in Watts.

32
Q

Define resistance.

A

The potential difference across a component, divided by the current in that component.

33
Q

What is resistivity proportional to?

A

It is proportional to the object’s resistance and cross-sectional area, and inversely proportional to the object’s length.

34
Q

What is the unit for resistivity?

A

Ohm metres.

35
Q

Do filament lamps act non-ohmic / ohmic for small values of current?

A

Ohmic.

36
Q

In a filament lamp, what occurs for resistance to increase as current increases?

A

The metal ions heat up, gaining kinetic energy, vibrating more, and so colliding more frequently with electrons, causing the resistance of the component to increase.

37
Q

In what way does resistivity act as a constant?

A

It links the resistance of the material with its AREA and LENGTH.

Physics (14 decks)

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