Flashcards in Electricity Deck (20)

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1

## What is charge measured in?

### Coulombs

2

## There are how many types of charges and list them

### Negative and positive

3

##
Unlike charges ...

Like charges ...

###
Attract

Repel

4

## What is an electric field?

### a region in which an electric charge experiences a force

5

##
Describe simple experiments to show the

production and detection of electrostatic charges

###
Get a balloon.

Inflate it.

Rub the balloon quickly on any dry surface e.g. a carpet.

Go to the nearest faucet/ water tap.

Turn it on.

Place the balloon close to but not touching the running water. ( see that the water bends towards the balloon)

6

##
State the direction of lines of force and

describe the field around a point charge and the field

between two parallel plates

###
A line of a force is the path of a free positive charge released in an electric field

The field around the point (diagram fig.11.2.2 pg 156)

The lines of force between 2 oppositely charged parallel conductors are parallel to another

7

## Definition of current, voltage and charge

###
Current: rate of flow of electrons, represents how much electric charge is passing a single point in the circuit in moment (A)

Voltage: energy per charge (V)

Charge: amount of positive/negative (Ohms)

8

##
Distinguish between the direction of flow

of electrons and conventional current

###
Direction of flow: from - to +

Conventional current: + to -

9

## Current equation (2)

###
I = V/R

I = Q/t

10

## Voltage current (2)

###
V = IR

V = E/Q (E is energy)

11

## Resistance

### R = V/I

12

## What is electromotive force (e.m.f)?

### energy supplied by a source in driving charge round a complete circuit

13

## Electrical energy equation

###
P = IV

no voltage: P = IxIR

no current: P = VxV/R

14

## How changes in p.d. or current affect resistance

###
↑ in Voltage = ↑ in resistance

↑ in Current = ↓ in resistance

15

## Relationship between resistance and length; resistance and cross-sectional area of a wire

###
To increase resistance, make the wire:

- Longer (length) => directly proportional

e.g. the longer the pipe, the more energy one must put into delivering water along its full length

-Thinner (diameter) => inversely proportional

e.g. the wider the pipe is, the easier it is to pump water through it and vice versa => make it thin

16

##
In a series circuit,...

Calculate combined resistance of two or more resistors in series

###
- Current is the same. I1 = I2 = I3

- Voltage is shared. p.d.s across the components in a series circuit is equal to the total p.d. across the supply. Vt = V1 + V2

- Resistance: Rt = R1 +R2

17

##
In a parallel circuit,...

Calculate combined resistance of two or more resistors in parallel

###
- Current: the current from the source is the sum of the currents in the separate branches. It = I1 + I2

- Voltage is the same

- Resistance: 1/Rt = 1/R1 + 1/R2

18

##
Describe the action of thermistors and lightdependent

resistors and show understanding of

their use as input transducers

###
- Transducers are devices that convert one type of energy into another.

- Thermistors :temperature increase => resistance decrease. Thermistors are often used as current limiting devices that help prevent over heating. Once the current gets to a certain limit (increasing heat lowers resistance, leads to increasing current), the circuit is broken to prevent overheating.

- Light-dependent resistors: increasing light intensity => lowering resistance. LDRs can be used on street lamps as input transducers. In this case, when it gets dark, the street lamps turn on.

19

## Describe the action of a variable potential divider

### Consists of 2 or more resistors in series connected to a fixed pd. Used to share/divide pd between resistors

20