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Fundamentals of EE > A level Electricity > Flashcards

A level Electricity Flashcards

1
Q

What is an electric current?

A

A flow of charge due to the passage of charged particles.

1A = 1C/1s

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2
Q

What is the charge of 1 electrons?

A

1.6x10‐¹⁹ C

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3
Q

How many electrons in 1C?

A

6.25x10¹⁸ e

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4
Q

What is a conventional current?

A

A current that moves from the positive to negative terminal.

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5
Q

What makes something an electric insulator?

A

The electrons are attached to the atom, so cannot move around freely when a voltage is applied.

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6
Q

What makes something a metallic conductor?

A

When the electrons are attached to the atom but some move when a voltage is applied.

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7
Q

What makes an electrolyte a conductor?

A

It has free moving delocalised positive and negative ions to carry a charge.

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8
Q

What makes something a semi conductor?

A

The number of charge carriers increases as the energy in the system increases.
( resistance decreases as temperature increases)

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9
Q

What is an intrinsic semi conductor?

A

Pure semiconductors materials as , electrons fully break free from atoms.

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10
Q

What is Kirchoff’s 1st law?

A

The Sum of electrons in the junction ( where electrons meet) = Sum of electrons out of the junction.

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11
Q

What is voltage?

A

An electric Force that pushes electrons. ( electrons move due to the potential difference)

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12
Q

How is voltage split across components?

A

Voltage is spread in the ratio of their resistances across components in series

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13
Q

What is the formula for voltage?

A

Voltage = work done / charge

1V = 1J / 1C

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14
Q

What are the 3 formulas of power?

A

V= voltage
I = current
R = resistance
P= Power

V * I = P
V = I * R
SO
I * R * I = P or I² * R
OR
V²/R

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15
Q

What is the property relating current direction and resistance?

A

Current always take the paths of least resistance.

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16
Q

Why is an ammeter series?

A

It has a very very low resistance so will have a small voltage across it.

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17
Q

Why is the voltmeter in parallel

A

The resistance is very very high so, there is a very small current.

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18
Q

How to calculate emf of a cell?

A

Plot a graph of voltage on y axis and current on x axis. The y intercept is the e.m.f

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19
Q

How to calculate internal resistance?

A

Plot a graph of potential difference of y axis and current on x axis. The gradient is -r.

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20
Q

What is the formula for Voltage (p.d)?

A

V = W/Q
The work done per unit of charge moved

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21
Q

What is mean drift velocity?

A

The average velocity of the electrons in a circuit

22
Q

What is the formula linking current and mean drift velocity?

A

I = nqvA

Current
=
the number of charge carriers per unit volume * the charge of each charge carrier
*the mean drift velocity * the cross-sectional area

23
Q

What is resistance?

A

A measure of how difficult it is to get current to flow through something

24
Q

What are the factors that determine resistance?

A

The length of a wire ( longer means more resistance)
The area of the wire (the wider, the easier it is for current to flow)
The resistivity of the material (The greater the resistivity the greater the resistance)

25
Q

What is the formula that relates resistivity to resistance?

A

R = pl/A
Resistance is = the resistivity * the length / the cross-sectional area

26
Q

What is resistivity?

A

Properties of a material that make it more difficult for current to flow .

27
Q

What is an ohmic conductor and therefore ohms law?

A

Ohm’s law is that - as long as the temperature remains constant, the current would be directly proportional to the p.d.
ohmic conductor is a conductor that follow ohm’s law.

28
Q

What does the ohms law mean for the resistance of an ohmic conductor?

A

The resistance of an ohmic conductor is CONSTANT.

29
Q

What are IV characteristics?

A

A graph which shows the current against the p.d and how a change in one leads to a change in the other,

30
Q

What are the IV characteristics of a metallic conductor?

A

A straight line, they are ohmic conductors and therefore have a constant resistance provided that temperature remains constant

31
Q

What are the IV characteristics of a filament lamp?
Why?

A

Steep curve but gets shallower as the p.d increases.
The current flowing through it causes the temperature to rise —-> in resistance.

32
Q

What is the relationship between the resistivity and temperature of a metal?

A

As the temperature increases the resistivity increases.
Heating up a metal means that more ions collide with electrons making it harder for them to move.

33
Q

What is a thermistor?

A

A resistor that’s resistance decreases as the temperature increases.
Also a type of semiconductor

34
Q

What is an LDR?

A

A resistor that’s resistance decreases as the light intensity increase.
Also a type of semiconductor.

35
Q

What is a diode?

A

A resistor that only lets current flow in one direction. Unless subjected to a very high voltage in the other direction.

36
Q

What is e.m.f?

A

The total amount of work the battery does on each coulomb of charge.
a.k.a the total p.d

37
Q

What is the formula for e.m.f

A

e.m.f = IR + Ir

38
Q

How would you work out the e.m.f of cells in series?

A

total e.m.f = emf1 + emf2+ emf3 …ect

39
Q

How would you work out the e.m.f of cells in parallel?

A

total e.m.f = emf1 = emf2 = emf3
This is because the current will split equally between the identical cells

40
Q

What is Kirchhoff’s first law?

A

Current flowing into a junction = current flowing out

41
Q

What is Kirchhoff’s second law?

A

The total emf = the sum of the p.d across each component.

42
Q

What formula is used to add the resistance in a series circuit?

A

Rt = R1 +R2 +R3 ect…

43
Q

What is the formula used to add resistance in parallel?

A

1/Rt = 1/R1 +1/R2 ect…

44
Q

What is the formula for the potential divider?

A

V(out) = R2* V (in) ÷
(R1+R2)

45
Q

What is a potentiometer?

A

A resistor (in the form of a long piece of wire) where the resistance is proportional to the length of the wire.
This also means that the p.d is proportional to the length of the wire

46
Q

What is the relationship between a potentiometer and the potential divider?

A

A potentiometer works similarly to a potential divider. But instead of having R1 and R2 you have a variable resistor with the length being changed to vary the resistance.

47
Q

What is the law of conservation of charge?

A

The charge cannot be created or destroyed and so in a closed loop the charge flow must be the same throughout

48
Q

Current in parallel?

A

Splits between branches, but due to conservation of charge, the supply current = sum of current in branches

49
Q

P.D. in series?

A

Split across components in the ratio of their resistances due to the law of conservation of energy

50
Q

P.d in parallel?

A

The supply p.d is the same as the p.d in each branch

51
Q

What is a potential divider circuit?

A

A pair of resistors used to spit the potential difference in a given ratio

Fundamentals of EE (7 decks)

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