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Physics > Electricity > Flashcards

Electricity Flashcards

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1
Q

Definition of electrical current

A

The rate of flow of positive charge

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2
Q

What is the definition of Drift Velocity?

A

The net movement of electrons parallel to current

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3
Q

What is the definition of potential difference?

A

Work done per unit charge

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4
Q

What is the definition of charge

A

Intrinsic property of matter that explains phenomenon

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5
Q

What is resistance?

A

Voltage divided by current caused by the same voltage. R = V/I

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6
Q

What is resistivity?

A

Resistivity is an intrinsic property of all materials

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7
Q

What is Kirchhoff’s first law?

A

Current is conserved at junctions

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8
Q

What is Kirchhoff’s 2nd Law?

A

In a closed loop, the sum of emf is equal to the sum of p.d.

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9
Q

What is the Electromotive force?

A

The amount of energy transferred from chemical to electrical energy. Joule transferred per Columb charge

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10
Q

What is Terminal potential difference ?

A

Potential Difference across terminals of a power supply when a current is flowing

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11
Q

What is electrical power?

A

Product of p.d. and current.

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12
Q

What is Ohm’s Law?

A

P.d. across a metallic conductor is proportional to the current through it, provided the physical conditions do not change

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13
Q

Why does an ammeter have 0 resistance?

A

In order to accurately measure the current through the components as any additional resistance will reduce current

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14
Q

Why does a voltmeter have infinite resistance?

A

So that an ammeter can accurately measure the current through a component as it is connected in parallel.

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15
Q

Why does resistance cause heating?

A
  1. Charge carriers repeatedly collide with the positive ions of the conducting material
  2. Net transfer of energy from the charge carriers to the positive ions
  3. Results in the positive ions gaining KE and vibrating more, increasing temperature
  4. Force due to p.d. across the material accelerates the charge carriers until they collide again
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16
Q

What is rate of heat transfer?

A

The power dissipated at the component.

17
Q

What is a potential divider?

A

Consists of two or more resistors in series with each other and with a fixed source of potential difference which is split between the components

18
Q

What are the uses of a potential divider?

A
  • Supply a p.d. which is fixed between 0 and source p.d.
  • Supply a variable p.d.
  • Supply a p.d. that varies with physical conditions
19
Q

How are the ratios of pd and resistance related for two resistors in series?

A

Ratio of pds of each resistor is equal to the resistance ratio of the two resistors.

20
Q

What are two examples of a variable pd potential divider?

A
  • Volume control, audio signal pd is supplied and variable output pd is supplied to loudspeaker
  • Brightness control, vary the brightness of a light source from 0 to normal brightness
21
Q

What are the advantages of a variable potential divider?

A

The output pd can be set to zero which is impossible when using a resistor and a variable resistor.

22
Q

What is a sensing circuit?

A

A circuit that produces an output pd which changes as a result of a change in a physical variable (temperature or light intensity)

23
Q

What is the purpose of a variable resistor in a sensing circuit?

A

The pd across the thermistor or LDR can be set to a desired value.

24
Q

What is a semiconductor?

A

A material in which the number of delocalised electrons increases with the temperature. Its resistance therefore decreases with temperature.

25
Q

What is a superconductor?

A

A wire or device made out of a material that has zero resistivity at and below a critical temperature.

26
Q

What is considered a high temperature superconductor?

A

Any material with a critical temperature above 77K, the boiling point of liquid nitrogen

27
Q

What are the uses of superconductors?

A
  • High power electromagnets that generate very strong magnetic fields used in MRI machines and particle accelerators
  • Power cables that transfer electrical energy without energy dissipation
28
Q

Why does heating increase resistance?

A
  1. Positive ions in the conductor vibrate more
  2. Charge carriers cannot pass as easily when a pd is applied
  3. Resistance increases
29
Q

What is a positive temperature coefficient?

A

When resistance increases with temperature

30
Q

What is a negative temperature coefficient?

A

When the resistance decreases with temperature

31
Q

Why does resistance of a semiconductor decrease with temperature?

A
  1. Electrons gain KE and brake away from the nuclei
  2. Number of charge carriers increases
  3. Resistance decreases
32
Q

Why are thermistors used in temperature sensitive sensors?

A

Their % change of resistance per change in temperature is much greater than for a metallic conductor.

Physics (4 decks)

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