# Unit 4: Electric Circuits

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## Description and Tags

It comprises an energy source typically a battery, one or more conducting materials, and circuit components such as resistors and capacitors

### 33 Terms

1

Current

The continuous flow of charge

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2

Average current

Iavg = change in charge/ change in time

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3

Battery

A battery is a device that maintains an electric potential difference between the two terminals.

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4

Direct current

The flow is from higher potential to lower potential. The electricity also flows in that direction called direct current.

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5

Resistance

It is the impedance to the flow of electricity through a material. Asa charge moves through a material, it eventually hits a non-moving nucleus in the material.

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6

Resistivity

It can be thought of as the density of nuclei the electrons may strike.

R = ρ l / A

• R = resistance of the circuit

• ρ = resistivity

• l = length

• A = cross-sectional area

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7

low resistivity

conductors

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8

high resistivity

insulators

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9

resistors in series

R eq = R1 + R2

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10

resistors in parallel

1/Req = 1/R1 + 1/R2

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11

Ammeter

An ammeter is a device with a very low resistance that measures the current.

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12

Voltmeter

It measures the electric potential called potential drop.

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13

Ohm’s Law

V = IR

• R is the resistance in the circuit.

• V is the potential difference in the circuit

• I is the electric current

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14

Power dissipation

P = VIP = I^2 RP = V^2 IR

• P is the power

• V is the potential difference in the circuit.

• I is the electric current.

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15

Kirchhoff’s rules

• The loop rule states that the voltage drop across any complete loop in the circuit is 0V.

• This statement follows from the conservation of energy when applied to circuits.

• The junction rule states that the sum of all current flowing into any junction is equal to the current flowing out of the junction.

• This statement follows from the conservation of charge.

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16

Capacitance

C = QV

• C = refers to the capacitance that we measure in farads

• Q = refers to the equal charge that we measure in coulombs

• V = refers to the voltage that we measure in volts

Besides, there is another formula that appears like this:

• C = refers to the capacitance

• K = refers to the relative permittivity

• ε0 = refers to the permittivity of free space

• A = refers to the surface area of the plates

• d = refers to the distance between places measured

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17

Capacitors in parallel

Cp = C1 + C2

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18

Capacitors in series

1/Cs = 1/C1 + 1/C2

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19

Altering the capacitance of capacitor

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20

Name four possible energy sources for a circuit

• Battery

• Photocell

• Electric Generator

• Thermocouple

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21

A circuit is opened and closed using a:

Switch

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22

What will happen to the charges in a circuit when a switch is closed?

The charges will flow through the circuit.

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23

What will happen to the charges in a circuit when a switch is open?

The circuit is broken and the charges stop flowing through the circuit.

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24

What is the standard voltage per branch in a home in the United States?

120 V

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25

A switch that automatically opens if the current is too high is a ________________

Circuit Breaker

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26

The symbol used to represent resistance in a schematic diagram is

a zigzag line

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27

A closed circuit is a circuit in which charge

can flow

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28

When two light bulbs are connected in series, the

same amount of current always flows through each bulb

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29

When resistors are put in parallel with each other their overall resistance is

smaller than the resistance of any of the resistors

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30

As more lamps are put into a series circuit, the overall current in the circuit

decreases

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31

As more lamps are put into a parallel circuit, the overall current in the circuit

increases

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32

When one light bulb in a parallel circuit containing several light bulbs burns out, the other light bulbs

burn the same as before

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33

Electrical devices in our homes are connected in

parallel

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