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SA H Physics > Electricity > Flashcards

Electricity Flashcards

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1
Q

What is the definition for current?

A

Current is the number of Coulombs of charge passing a point in one second.

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2
Q

What is the definition of 1 amp?

A

1 Coulomb of charge passing a point in 1 second.

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3
Q

What is potential difference?

A

The number of Joules of energy transferred per Coulomb of charge.

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4
Q

What is 1 volt?

A

1 Joule of energy transferred per Coulomb of charge

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5
Q

What is the value of the mains supply?

A

230V, 50Hz

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6
Q

What is meant by the Root Mean Square Voltage? (Vrms)

A

It is the value of an a.c. voltage that will deliver the same amount of energy as a d.c. voltage.

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7
Q

What can be said when comparing Vrms to Vpeak?

A

Vpeak is always greater than the Vrms

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8
Q

When calculating power should you use Vpeak or Vrms?

A

Vrms

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9
Q

What is the definition for e.m.f?

A

The number of Joules of energy given to each Coulomb of charge passing through the cell.

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10
Q

Give two sources of e.m.f

A
  • chemical cell
  • Thermocouple
  • Piezo-electric generator
  • Solar cell
  • Electromagnetic generator
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11
Q

What is the terminal potential difference, Vtpd?

A

It is the potential difference which is able to supply the user when the circuit is complete and current flows.

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12
Q

What are the lost volts, Vlost?

A

This is the potential difference unavailable to the user because of the internal resistance of the supply.

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13
Q

In the following circuit what quantity will the voltmeter measure and why?

A

The e.m.f as NO current is flowing as the circuit is incomplete.

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14
Q

In the following circuit what quantity will the voltmeter measure and why?

A

The Vtpd as there is a complete circuit and current is flowing so, some voltage will be lost.

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15
Q

What is the short circuit current?

A

The maximum current a supply can give - this is achieved when the terminals of the supply are joined with a short thick wire ( almost no external resistance)

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16
Q

From the graph, how can you calculate the internal resistance of the cell?

A

internal resistance = - gradient

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17
Q

From the graph, how do you find the e.m.f. ?

A

When the current = 0A. Find point on graph where current = 0A, read off corresponding voltage.

18
Q

From the graph, how do you find the short circuit current?

A

When the Potential difference = 0V. Find this point on the graph, read off the corresponding current.

19
Q

What is capacitance?

A

The charge stored per volt.

20
Q

What is meant by 1 Farad?

A

1 Coulomb of charge stored per volt

21
Q

What could be altered in the circuit below to increase the charging time of the capacitor?

A
  • Increase the resistance of the resistor
  • Increase the capacitance of the capacitor
22
Q

What could be altered in the circuit below to decrease the charging time of the capacitor?

A
  • Decrease the resistance of the resistor
  • Decrease the capacitance of the capacitor
23
Q

From this energy level diagram, what type of material is being represented?

A

Insulator

24
Q

Describe the shape of a graph of voltage across capacitor against time for charging a capacitor.

A

Starts from 0V. Increases to the supply voltage.

25
Q

Describe the shape of a graph of voltage across capacitor against time for discharging a capacitor.

A

Starts from the supply voltage Decreases to 0V.

26
Q

Describe the shape of a graph of current in a capacitance circuit against time for charging a capacitor.

A

Starts from a maximum value and decreases to zero.

27
Q

Describe the shape of a graph of current in a capacitance circuit against time for discharging a capacitor.

A

Starts from a maximum value and decreases to zero, current is in the opposite direction from the charging current.

28
Q

From this energy level diagram, what type of material is being represented?

A

Semiconductor

29
Q

From this energy level diagram, what type of material is being represented?

A

Conductor

30
Q

Explain how a pure semiconductor conducts.

A

Conduction band is empty. Valence band is full. There is a small energy gap. If the temperature is increased the electrons in the valence band can gain enough energy to jump the gap into the conduction band. These electrons are free to move and so conduction increases.

31
Q

Explain how an n-type semiconductor can be created.

A

The semiconductor has impurities added that have five electrons in its outer shell. Four of these are used to fill the valence band. The fifth electron is in the conduction band. This is free to move and so conduction increases.

32
Q

Explain how a p-type semiconductor can be created.

A

The semiconductor has impurities added that have three electrons in its outer shell. These three do not completely fill the valence band. So there are electrons free to move in this band so conduction increases.

33
Q

How is the internal electric field created in a pn junction?

A
  • Electrons from the conduction band of the n-type move into the conduction band of the p-type and drop into the valence band of the p-type material.
  • This leaves the n-type material slightly positively charged and the p-type material slightly negatively charged around the junction.
  • This creates a potential difference which gives an electric field.
  • The electrons in the conduction band of the n-type, do not have enough energy to overcome the potential difference of the electric field, to pass into the conduction band of the p-type.
34
Q

How is a p-n junction connected in forward bias?

A

Connect n-type to negative of supply connect p-type to positive of supply

35
Q

How is a p-n junction connected in reverse bias?

A

Connect n-type to positive of supply Connect p-type to negative of supply

36
Q

Explain why a forward biased p-n junction conducts.

A
  • Energy is supplied to the n-type material by the battery
  • The effect of this is to reduce the potential difference of the electric field.
  • The electrons in the conduction band of the n-type now gain enough energy to overcome the internal electric field and pass into into the conduction band of the p-type.
  • The p-n junction will conduct.
37
Q

Explain why a reverse biased p-n junction will not conduct.

A
  • Energy is supplied to the p-type material by the battery.
  • This increases the internal electric field strength.
  • The electrons in the conduction band of the n-type do not have enough energy to overcome the larger potential difference of the electric field.
  • Electrons cannot pass into the conduction band of the p-type so the p-n junction will not conduct.
38
Q

Explain how an LED produces light.

A
  • When the LED is forward biased. Energy supplied to the electrons in the n-type conduction band by the battery.
  • The electrons now have enough energy to overcome the internal electric field and move through the electric field into the empty conduction band of the p-type semiconductor material.
  • The electron then drops from the conduction band of the p-type to the valence band of the p-type.
  • The electron gives out the energy as a photon of light as it drops into a lower energy band.
39
Q

In which mode is this operating?

A

Photoconductive

40
Q

In which mode is this operating?

A

Photovoltaic

41
Q

Explain what happens to the reading on the voltmeter when the circuit is changed from figure 1 to figure 2.

A

Resistance in the circuit decreases.

Current in the circuit increases.

Lost volts will increase Vlost = Ir

E - Vlost = Vtpd

So the reading on the voltmeter will decrease as it measures the Vtpd.

42
Q

Explain how a photovoltaic cell produces an electric current.

A
  • A photon is absorbed by an electron in the valence band of the p-type material.
  • If this energy is high enough the electron can jump into the conduction band of the p-type.
  • The electron experiences a force from the internal electric field.
  • The electron is moved through the electric field to the conduction band of the n-type.
  • This creates a current.

SA H Physics (4 decks)

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