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AS Level CIE physics > Electricity > Flashcards

Electricity Flashcards

1
Q

Define electric charge

A

Electric charge= electric current x time
Q=It
Q=AS (Coloumb)
I=A
t=s

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2
Q

Give another formula for electric charge

A

Electric charge=number of charged particles x charge on each particle
Q=Nq
Q=As (Coloumb)
N=no unit
q=Coloumb

Q=nAlq
n= number density
A=Area
l=length
q=charge on each carrier

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3
Q

What is the value of elementary charge?

A

e is elementary charge and its value is 1.6x10-19 C.

C is coloumbs

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4
Q

What is the charge of an electron, positron or proton particle?

A

If each particle is electron, positron or proton they have same charge which is equal to elementary charge.
Charge on electron=-e
Charge on positron=charge on proton=+e

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5
Q

What is the formula for charge density or number density?

A

Number Density=number of charged carriers/volume
n=N/V
n=m^-3 (per meter cube)
N=no units
V=m^3

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6
Q

What is the function of number density?

A

Number density describes how good or bad a conductor is.
Higher the number density better is the conductor.

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7
Q

What is another name for charged carriers?

A

Charged carriers are also called free electrons, delocalised electrons. These electrons can easily slip on the lattice of metal crystals formed by layers of metal particles.

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8
Q

What is drift velocity?

A

Speed at which charge carriers are drifting through conductor is called drift velocity.

Drift velocity=Distance moved by charged carrier/time taken
Vd=l/t

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9
Q

What is a conductor?

A

A conductor is anything that transfers charge from one point to another.

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10
Q

What is drift?

A

The motion of charged carriers (electrons) through a conductor is called drift.

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11
Q

What is the relationship between drift velocity and current.

A

Vd∝I

I=Current

Vd=drift velocity

Important for deriving formula

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12
Q

What is the relationship between Drift Velocity and cross sectional area of a conductor?

A

Vd∝1/A

A=cross sectional area of a conductor

Vd=drift velocity

Imporatnt for deriving formula

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13
Q

What is the relationship between number density and drift velocity?

A

Vd∝1/n

Vd=drift velocity and n=number density

Imporant for deriving formula

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14
Q

What is the relationship between charge on each carrier and drift velocity?

A

Vd∝1/q

Vd=drift velocity
q=charged carrier

Imporatnt for deriving formula

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15
Q

What factors affect drift velocity and what formula can we derive from their relationship?

A

Current
Cross sectional area of a conductor
Number density
Charge on each carrier
If it is the same conductor all the above variable will stay the same.

Vd=I/AnQ

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16
Q

What is the formula of a prism?

also volume of a cyllinder

A

Volume of a prism=Base area x height
V=Al
A=area
L=height

Volume of a cylinder=1/4 x π d^2 h

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17
Q

What is the formula of the area of circular wires?

A

A=πd^2/4

therefore Vd=4I/πd^2nq

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18
Q

What is current?

A

Current is the flow of charge. Role of current in a circuit is to pick up and drop off energy. Current does not get consumed. Symbol for current is I. Unit for current is ampere. Current is a scalar quantity.

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19
Q

What is the direction of current?

A

Direction of current is also called conventional current, which is either along the direction of movement of positive charge or opposite to the direction of negative charge.

Although direction of current is big issue, it is a scalar quantity.

20
Q

What is electric potential?

A

Electrical work done per unit charge is called electrical potential.

Electrical potential=Electrical work done/Electric charge

V=W/J
W=J
Q=C
V=JC^-1

21
Q

What does electric potential of one volt mean?

A

Electric potential of one volt means work done of one joule done by/on a unit charge.

22
Q

What is electric potential difference?

A

Difference of energy per unit charge at two different points in a circuit is called potential difference.

23
Q

What is the name given to potential difference across a resistor or a lamp?

A

Potential difference across a resisitor or lamp is simply called potential difference.

24
Q

What is the name given to potential difference across a battery or cell?

A

Potential difference across a battery or cell is called voltage or terminal potential.

25
Q

What instrument measures potential difference?

A

Voltmeter measures potential difference.

26
Q

What instrument measures current?

A

Ammeter measures current.

27
Q

What does emf stand for?

A

Emf:- Stands for electromotive force (not a force).

28
Q

Define EMF.

A
  • Work done on unit charge by the cell to move it across the whole circuit is called emf.
    OR
  • Energy converted from chemical energy to electrical energy in a cell is called emf of the cell.

potential difference measured by voltmeter across battery/cell is emf.

29
Q

Is current consumed in any point of the circuit?

A

Current is not consumed in any component of the circuit. Current does pick and drop off service for energy in a circuit. It picks up energy from supply: Cell or battery and drops it at resistor, fan, lamp, motor etc.

For any component current entering=current leaving. Only difference is energy per unit charge is different.

(remeber example of truck)

30
Q

What is Ohms law?

A

According to Ohm’s law:
Current through a resistor is directly proportional to potential difference across the resistor, provided if temperature remains constant.

Potential Difference ∝ Current
V∝I

31
Q

What formula can be derived from ohm’s law?

A

Potential difference ∝ Current
v∝I
v=IR
V=potential differnce in volts
I=Current in amperes
R=Resistance in Ohms (Ω Omega)

32
Q

What is the formula conecting power, current and resistance?

A

P=VI
P=I^2 R

33
Q

What is the formula connecting Energy, volts, current and time?

A

E=VIt
E=energy
V=volts
I=current
t=time in seconds

34
Q

What is the formula connecting energy, current, time and resistance?

A

V=IR(formula from ohms law) and V=E/Q(formula for electric potential)
V=E/IT (Q=It)
E/IT=IR
E=I^2Rt

35
Q

Define electric resistance.

A

In some materials it is easy for electrons to drift and in some it is more difficult. Some materials offer more opposition than others to the flow of charge through them, this opposition is called electrical resistance.

36
Q

What is the relationship between a conductor and a resistor?

A

Good conductors offer less resistance.
Bad conductors offer more resistance.

37
Q

What is electric resistance measured in?

A

Electric resistance is measured in Ohms.

38
Q

What is the formula for electrical resistance?

A

R=V/I
R=Resistance(Ohm)
V=Voltage (Jc-1)
I=Current (As)

Therefore one ohm=one volts per one ampere.

39
Q

What factors affect electrical resistance?

A

Factors that affect electical resistance are:
1. Length of the conductor
2. Cross sectional area of the conductor
3. Nature of material of conductor
4. Temperature of conductor

40
Q

Describe the relationship between electrical resistance and length of the conductor.

A

Longer the conductor greater the resistance.
Resistance is directly porportional to length of the conductor.
R∝L

41
Q

What is the relationship between cross sectional area and electrical resistance?

A

Wider conductors have small resistance.
Resistance is inverseley porportional to cross sectional area.
R∝1/A

42
Q

What is the relationship between the nature of the material of the conductor and electrical resistance?

A

Resistivity is used to classify conductors. Good conductors have smaller resistivity.

43
Q

What is the relationship between temperature of the conductor and electrical resistance?

A

In case of metal conductors resistance increases with increase of temperature.
In case of a semiconductor thermistor, resistance decreases with increase in temperature.

44
Q

What is the formula of resistivity which can be derived from the factors which affect resistance?

A

R∝L + R∝1/A + R∝L/A
so R=ρ l/a
Where ρ is resitivity and used as a constant of porportionality.

45
Q
A

AS Level CIE physics (8 decks)

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