4.2 Energy, Power And Resistance Flashcards Preview

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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

What is conservation of charge?

the law stating that charge can't be created nor destroyed, it can only be transferred and the total will always be constant