Chapter 18

Question 1

Battery

Answer 1

Produces constant voltage to make charges move (current)

1. Electrons free to move in conductors → carry energy through circuit.
2. Energy comes from a battery (converts chemical → electrical energy)
3. As energy is transformed, a potential difference V develops across the battery’s terminals (called EMF).

Question 2

Current

Answer 2

amount of charge that passes through an area in a given amount of time

units: Amps → (1A = C/s)

Question 3

Equations for current (I)

Answer 3

Question 4

Current in a metal wire is proprotional to what?

Answer 4

Current (I) proportional to potential diff (V) applied to its 2 ends

Question 5

Electrode

Answer 5

plates/rods (made of dissimilar metals)

Question 6

Electrolyte

Answer 6

solution (ie a dilute acid)

Question 7

Terminal (battery)

Answer 7

part of electrode outside of solution (where you connect wires/circuits)

Question 8

What is the simplest BATTERY made of?

Answer 8

2 electrodes (+ and –) & 1 electrolyte

Question 9

Ciruit

Answer 9

continuous conducting path connected between terminals of a battery

Question 10

Complete Circuit

Answer 10

continuous conducting path

Question 11

Open circuit

Answer 11

break in circuit (ie. cut wire)

Question 12

Ground

Answer 12

common conductor (provides continuity)

Question 13

Conventional current

Answer 13

current direction in a circuit = direction + charge would flow

Question 14

Resistance

Answer 14

opposition to flow of charge

units: ohms → (1 Ω = 1 V/A)

Question 15

In a device that produces heat (ie. toaster) what kind of resistance do you want?

Answer 15

HIGH resistance needed (otherwise no heat produced)

Question 16

Do you want low/high resistance in wires?

Answer 16

LOW resistance wires (to minimize energy loss)

Question 17

Resistance of a uniform wire EQUATION

Answer 17

p = constant of proportionality (RESISITIVITY) → units (Ω m) → depends on material used

Question 18

What is special about silver?

Answer 18

It has the lowest resistivity (p), therefore lowest resistance (R) making it best conductor → electrons free to move

Question 19

Ohm’s Law EQUATION

Answer 19

V = IR

Question 20

To what materials can Ohm’s law be applied?

Answer 20

Ohmic materials: metal conductors (R is constant) whose temperature doesn’t change much

Question 21

What are resistors used for?

Answer 21

used to control (reduce) the amount of current in a circuit

Question 22

What factors does resistance depend on?

Answer 22

type of material wire made of, length, cross sectional area

Question 23

Electrical conductivity

Answer 23

amount of current a material can carry

(reciprocal of resistivity)

Question 24

Electrical conductivity EQUATION

Answer 24

Question 25

How does temperature effect resistance?

Answer 25

R of metals INCREASES at higher temp

(because atoms move faster and interfere more with flow of electrons)

Question 26

Power

Answer 26

amount work down / time

rate energy is transformed

Question 27

Power EQUATIONS

Answer 27

P = IV

P = W/t

Question 28

Do thicker wires have less or more resistance?

Answer 28

less R

Question 29

Fuses/circuit breakers

Answer 29

switches that open the circuit when current exceeds a safe value to prevent overloading

Question 30

Open circuit

Answer 30

no longer a complete conducting path (no current can flow)

as if R = infinity

Question 31

Short ciruit

Answer 31

two wires touched that shouldn’t have

Question 32

Q: Why shouldn’t properly rated fuses be replaced by higher-rated ones?

Answer 32

Fuse won’t blow as intended and high current will harm (ie. melt) whole circuit…

Question 33

Direct Current (DC)

Answer 33

one-directional flow of electric charge

(battery example)

Question 34

Alternating current

Answer 34

reverse direction many times/sec (sinusoidal)

Question 35

Rectifier

Answer 35

AC → DC current

Question 36

Inverter

Answer 36

DC → AC