Flashcards in 4.2 Energy, Power And Resistance Deck (35)

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1

## Define emf.

### Of a supply, the energy gained per unit charge by charges passing through the supply, when a form of energy is transferred to electrical energy carried by the charges. Measured in v or jc

2

## Define pd.

### Measured across a component, energy transferred per unit charge by the charges passing through the component.

3

## Define Resistivity.

###
The resistance offered by a unit length of wire made of a material having a cross sectional area of one unit.

=RA/l and define terms.

4

## Define power.

### The rate at which work is done.

5

## Define electron drift velocity.

### The average displacement travelled of the electron along the wire per second. On average they move slowly in one direction through the metal lattice, when a pd is applied because they collide constantly.

6

## Define elementary charge.

### Charge on a single electron, -1.6x10^-19

7

## Conventional current

### The direction of flow of current from positive to negative, opposite to the flow of electrons, original idea behind flow of charge.

8

## Diode

### Allows current to only flow in one direction

9

## Forward bias

### Forward bias is when current flows in the direction allowed by the diode.

10

## Reverse bias

### Flow of current against the direction of the diode

11

## Internal resistance

### The resistance within a voltage source that causes a lower volte supply that expected when current flows

12

## Current

### Rate of flow of charge, the charge flowing through a given point per second

13

## What is Kirchhoff's first law

### As charge is always conserved, the sum of charges flowing into a junction must be equal to the sum of the charge leaving it, the same is true for current

14

## Equation for drift velocity and factors in equation?

### I=nAve

15

## Conductors

### Larger number of free charger carriers per unit volume

16

## Insulators

### Very few free charge carriers per unit volume

17

## Ohms law

### The current through a conductor is directly proportional to the potential difference across it, provided the temperature is constant

18

## Factors that affect electrical resistance

###
-Material of wire

-Length

-Cross sectional area

-Temperature of wire

19

## How does length of wire affect resistance?

### p.d is more spread amongst electrons

20

## How does cross sectional area affect resistance?

### More electrons to flow at same drift velocity

21

## How does temperature of wire affect resistance?

### Resisting ions have more energy to vibrate

22

## I-V characteristics of a resistor

### Directly proportional

23

## I-V characteristics of a filament lamp

###
Low current= ohmic conductor

High current, resistance increases due to more collisions and higher temperature

24

## I-V characteristics of a diode

### Require a threshold voltage for conduction to occur, current only in forward bias.

25

## Define resistivity.

### The measure of the resistance of a material for its cross-sectional area per unit length of wire.

26

## Equation for resistivity

### RA/I

27

## Define temperature coefficient.

### Value representing the relationship between the change in resistance and change in temperature of a conductor/semi conductor

28

## Define electrical power

### Rate at which energy is converted to or from electrical energy to or from another form

29

## Power equations

###
Power = work done /time

Power = current^2 x resistance

Power = voltage^2 / resistance

30