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Hint

1

electric circuit

A continuous and closed path of electric current.

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2

Electrical current

Electric current is expressed by the amount of charge flowing through a particular area in unit time.

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3

S.I unit of current

ampere, A

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4

Current formula

I=Q/t

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5

S.I unit of charge

Coulomb, C

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6

Ammeter

an instrument for measuring electric current in amperes.

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7

Charge formula

Q = It

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8

One couloumb

charge in 6 X 10^18 electrons

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9

One electron

-1.6x 10^-19 C

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10

Potential difference is produced by

battery

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11

Potential difference

Potential difference between two points in an electric circuit carrying some current is the work done to move a unit charge from one point to another.

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12

V =

W/Q (energy/charge)

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S.I unit of potential difference

V (Volt)

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15

1V

1J/C

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16

Volmeter

A device used to measure voltage, or electrical potential energy difference

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17

Ohm's Law

The potential difference, 'V' across the ends of a given metallic wire in an electric circuit is directly proportional to the current flowing through it provided the temperature remains the same

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18

Ohms law formula

V = IR

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19

Resistance

The property of a conductor to resist the flow of charges through it.

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20

S/I unit of resistance

Ω Ohm.

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21

If the resistance is doubled

the current will be halved

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22

Variable resistance

A component used to regulate current without changing the source of the voltage.

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Rheostat

A device which can vary the resistance without opening the circuit

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24

Factors on which resistance depends

Length, Area of cross section, Nature of its material

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Motion of electrons through a conductor

is retarded by its resistance. Low resistance, good conductor. High resistance, poor conductor.

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Resistor

An electrical device that resists the flow of electrical current due to its appreciable resistance.

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27

R =

p l/A

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Resistivity

The electrical resistance of a conductor of unit cross-sectional area and unit length.

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29

S.I unit of resistivity

Ωm

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30

Series connection- potential difference

V= V1 + V2 + V3

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Series connection- resistance

R= R1 + R2 + R3

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32

Disadvantages of series connection

Different appliances requiring different levels of current cannot be connected. If one component fails, the entire circuit breaks.

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33

Parallel connection resistance

The reciprocal of the equivalent resistance of a group of resistances joined in parallel is equal to the sum of the reciprocals of the individual resistances. 1/R = 1/R1 + 1/R2 + 1/R3

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Advantages of parallel connection

If one of the components fails, the others still work. Each component receives the required amount of current since they are in different branches.

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35

Heating effect of electric current

If the electric current is purely resistive, the source energy gets dissipated in the form of heat.

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Power

P = VI

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Heat

H = I^2Rt or VIt

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38

Joule's law of heating

The heat produced in a resistor is directly proportional to the square of current for a given resistance, directly proportional to the resistance for a given current and directly proportional to the time for which current flows through the resistor.

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39

incandescence

the emission of visible light by a hot object

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40

If resistance increases

temperature increases

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41

Filament

Should have a high melting point, have high resistance and be thermally isolated

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Power

The rate at which electric current is dissipated or consumed in an electric circuit.

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P

V^2/R or P = VI

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S.I unit of power

W

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1W

1Vx 1A

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Kilowatt

1000W

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Wh

1 watt of power for 1 hour

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kWh

1000 watt x 3600 second or 3.6 x 10^6 J

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W=

VIt

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Examples of filament

Tungsten - highest melting point and high resistivity

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51

Fuse is made of

Al, Cu, Fe alloy

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Metal used for electrical heating devices

Nichrome as it is an alloy, therefore has higher melting point, higher resistance and does not oxidise.

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53

Rating of electrical appliances

The voltage at which the appliance functions and the rate of consumption (power) of that voltage.

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54

Energy si unit

Joules (J)

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Energy =

Power x time

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resistance is directly proportional to

length, temperature

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resistance is indirectly proportional to

area of cross section

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