what is current

the rate of flow of charge

meausre in Amperes (Amps)

in which direction does current flow in a circuit?

from the positive terminal to the negative terminal

(the delocalissed elecrtrons move about in the opposite direction)

can charges be positive and negative or just one?

they can be both

positive - like in a gas

negative - like deloalised electrons in a metal

what is the equation that links charge, current and time?

charge (coloumbs) = current (Amps) x time (seconds)

I = Q ÷ t

Q = I x t

what is charge measured in?

coulumbs (c)

how many electrons are in 1 coulomb of charge?

6.25 x 10^{18} electrons

how many coloumbs are there in 1 Amp?

1 coloumb per second

where is an ammeter always placed in a circuit?

in series with the device

A_{1} = 0.18 Amps

what is the Amps of A_{2} and A_{3}

why?

A_{2} = 0.18 Amps

A_{3} = 0.18 Amps

there s an equal amount of amps all aound the circuit

the current is consant

A_{1} = 0.34 Amps

what is the Amps of A_{2 }and A_{3}?

why?

A_{2} = 0.17 Amps

A_{3} = 0.17 Amps

the current is split in half

A_{2} + A_{3} = A_{1}

what happens to the rate of current when there is more resistance in a circuit?

it decreases

what happens to current at a junction?

current splits

current always chooses the easiest route

V_{1} = 2.73 volts

V_{2} = 1.00 volts

what is V_{3} ?

why?

V_{3} = 1.73 volts

V_{2} + V_{3} = V_{1}

what happens to V_{2} when you remove one of the bulbs?

the voltage increases

what happens to V_{2} when you remove a cell

the voltage decreases

V_{1} = 1.65 Volts

what are V_{2} and V_{3} ?

why?

V_{2} = 1.65 volts

V_{3} = 1.65 volts

they all have the same amount of volts

complete the data for all of the A_{n} knowing:

A_{3} = 2.5 Amps

A_{5} = 1.5 Amps

A_{6} = 2.0 Amps

A_{1} = 6.0 Amps

A_{2} = 6.0 Amps

A_{3} = 2.5 Amps

A_{4} = 3.5 Amps

A_{5} = 1.5 Amps

A_{6} = 2.0 Amps

A_{7} = 3.5 Amps

A_{8} = 6.0 Amps

an ammeter reads 0.8A

how much charge flows through it in 0.5 seconds?

I = Q ÷ t

Q = I x t

= 0.8 x 0.5

= 0.4 C

0.3 Coulombs of charge flows through a lamp in 0.2 seconds

what current flows through it?

I = Q ÷ T

= 0.3 ÷ 0.2

= 1.5 A

an ammeter reads 3.2 A

how long will it take 2.0 C to flow through it?

I = Q ÷ t

t = Q ÷ I

2.0 ÷ 3.2

= 0.625 secs

an ammeter reads 0.65A for 1 minute

how much charge flows through it?

I = Q ÷ t

Q = I x t

= 0.65 x 60 ( 1 minute = 60 secs)

= 39 C

a lightning strike from a cloud lasts for 0.75 seconds and delivers a current of 30kA

how much charge does the cloud lose?

I = Q ÷ t

Q = I x t

= 30,000 x 0.75

= 22500 C

what is voltage?

the amount of work done (energy) per coloumb of charge

what is the equation for voltage?

voltage (Volts) = work done (Joules) ÷ charge (Coulumbs)

how many Joules per Coulombs are there in in 1 Volt?

1

this means 6.25 x 10^{18} electrons would have 1 Joule of electrical energy

the greater the voltage, the .... the amount of energy 1 Coulomb of ... has

the greater the voltage, the **greater** the amount of energy 1 Coulomb of **charge** has

what do voltmeters measure?

potential difference (pd)

measured in volts

cells are a source of ....

they have .... inside them (acid) that ... with different ...

this reaction converts ... energy into ... energy

cells are a source of **energy**

they have **chemicals** inside them (acid) that **react** with different **metals**

this reaction converts **chemical** energy into **electrical**energy

a 1.5V Cell is capable of converting ... Joules of ... energy into ... Joules of ... energy

a 1.5V Cell is capable of converting **1.5 **Joules of** chemical **energy into **1.5** Joules of **electrical** energy

how does a voltmeter work out the potential difference?

the cell is rated at 1.5V

a cell rated at 1.5V means it gives 1.5J of eletrical energy to each coulomb that flows through the circuit

as the coulomb approaches the resistor, the voltmeter measures that it has 1.5J of electrical charge

the coulomb then flows through the resistor, where it does its work

the electrical energy is converted into thermal energy

the coulomb flows out of the resistor with no electrical energy

the voltmeter measures that the coulomb has 0.0J of electrical energy when it leaves the resistor

1.5 J/C - 0.0 J/C = 1.5V

the potential difference is displayed by the voltmeter

given that V_{1} = 3.0 V what is V_{2}, V_{3} and V_{4}?

_{V2 }= 3.0V

V_{3 }= 3.0V

V_{4 }= 3.0V

given that V_{2} = 1.5V, V_{3} = 1.5V and V_{4} = 1.5V, what is V_{1}?

V_{1} = 4.5V

consider a coulomb of charge in the cell

it has 4.5J of electrical energy when it leaves the cell and moves around to position A in the circuit

position A has 4.5J (Coulomb energy)

how much Coulomb energy does B, C and D have?

V_{1} = 4.5

V_{2}, V_{3}, V_{4} = 1.5

B = 3 J

C = 1.5 J

D = 0 J

what is the equation that links current, potential difference, time and work done?

Q = I x t

V = W ÷ Q

V = W ÷ I x t

I x t = W ÷ V

W = V x I x t

what is an easy way to remeber the equation that links current, potential difference, time and work done?

W = I x t x V

Itv (the show!)

if the emf of a cell is 3.0V, how much energy is converted into electrical energy if it supplies 5C of charge?

voltage = J ÷ C

J = voltage x C

= 3.0 x 5

=15J

if a 1.5V cell delivers 2.0A for 10 seconds, how much electrical energy does it convert?

energy = voltage x charge

= 1.5 x (2.0 x 10)

= 30J

what does varying the resistance of a variabe resistor do to the potential difference?

it will vary the potential differnce (voltage) across the resistor

what is the symbol for a resistor?

what is the symbol for a variable resistor?

what does Ohm's law state?

current (I) and voltage (V) are directly proportional provided that other physical properties (like temperature) remain constant

according to Ohm's law, what will an I-V graph look like?

a straight line through the origin

on a graph, does a higher resistance has a bigger or smaller gradient?

smaller gradient

according to Ohm's law, does a higher resistor have a higher or lower current?

lower

as resistance increases, current **...**

as resistance increases, current **decreases**

what is the equation for Ohm's law?

voltage (v) = current (A) x resistance (ohms, Ω)

V = IR

what is the symbol for ohms?

Ω

does a filament lamp obey ohm's law? why?

no

current and voltage are not directly proportional

explain why we get his curve on the I-V graph for a filament lamp

the resistance for B gets larger as the lamp gets hotter (thermal energy - energy disipated from circuit) as it gets brighter

the positive ions (which metals are made up of) vibrate more

the lower the gradient the higher the resistance

the terminals of the power supply on a circuit for a filament lamp are reversed which produces data O

--> C

does the filament bulb's characteristics change due to the change in current dicrection?

no

in this experiment, the direction of current does not change thecharacteristics of the bulb - it doesn't matter

has rotational symmetry

what is inside a metallic conductor?

a flow of negatively charged electrons

where does a voltmeter go in a circuit?

across what you are investigating

what does L.D.R. stand for?

light dependant resistor

what is the symbol for a L.D.R?

how do you set up an experiment to record the resistance of a L.D.R.?

shine a light on the L.D.R. and record the resistanve using the ohm-meter

place tracing paper between the lamp and the L.D.R. to reduce the light intensity ad record the resistance of the L.D.R.

how does resistance vary with light intensity?

as light intensity increases, resistance decreases

as light intenisty decreases, resistance increases

what is the symbol for a thermistor?

as temperature increases, the resistance of the thermistor ...

decreases

resistance and temperature are ...

what does this look like on a graph?

inversely proptional

a thermistor is the only resistor wherere when temperature increases, resistance ... - every other resistor ...

a thermistor is the only resistor wherere when temperature increases, resistance **de****creases**- every other resistor **increases**

what is the symbol for a diode?

if current flows

conducts

if current flows ---> then the diode ...

does not conduct

what does the circuit look like to test the current and voltage across a diode?

what does an I-V graph look like in an experiment including diode

explain

in reverse bias the current in very low therefore the resistance is very high

in foward bias the current is high therefore the resistance is low

current suddenly increase at 0.7 volts (resistance suddenly decreases)

a student wants to vary the pd across a 2Ω resistor to record how the current varies with pd

how does the student vary the pd usingjust the equiptment in the circuit?

changing the value of R_{h}

the voltmeter reads 4.5V and the resistance is 2 ohms

what current is recorded by the Ammeter?

V = I x R

I = V ÷ R

= 4.5 ÷ 2

= 2.25 Amps

given that the voltmeter reads 4.5V, what is the pd across the variable resistor when he cells is 6V?

6V - 4.5 V = 1.5 V

given that the pd across the variable reistor is 1.5V and the current is 2.25 Amps, what is the resistance (R_{h}) of the variable resistor?

V = I x R

R = V ÷ I

= 1.5 ÷ 2.25

= 0.6 Ω

the student wants only L_{3} to work

which switches should she close?

S_{1}

S_{4}

S_{5}

the same 6V battery is used to power 3 identical light bulbs in a parallel ciruit

what is the pd across L3

6V

the same 6V battery is used to power 3 identical light bulbs in a parallel ciruit

if the current flowing through the lamp is 2.0A, what is its resistance?

V = I x R

R = V ÷ I

= 6 ÷ 2

= 3 Ω

name two advantage of a parallel circuit

failure of one component does not lead to the failure of the other components

more components may be added or taken away and it will hardly affecr the others

CHECK

name an disadvantage of a parallel circuit

each bulb glows less brightly because current is shared

CHECK

explain why a filament lamp's I-V characteristics are as shown

the filament lamp does not obey Ohm's law as the current and voltage are not directly proportional

we get the curve shape because the resistance for B gets larger as the lamp gets hotter (thermaln energy) as it gets brighter

the graph shows an inverse relationship as the gradient gets lower as the resistance gets higher

as current increases, temperature increases

the terminals of the power supply are reversed which produces data 0-C

the filament lamp has rotational symmetry

How do you change the current so it flows in a negative direction?

swap the wires around so they are attracted to opposite terminals

what is the symbol and unit for voltage?

symbol = V

unit = volts

what is the symbol and unit for current?

symbol = A

unit = amps

what is the symbol and unit for charge?

symbol = I

unit = coulombs

what is the symbol and unit for resistance?

symbol = R

unit = ohms/ Ω

A circuit contains 3 identical bulbs in parallel. The power supply is 12V and each bulb has a resistance of 6Ω

calculate the current flowing through one of the lamps

current = voltage ÷ resistance

= 12 ÷ 6

= 2 Amps

A circuit contains 3 identical bulbs in parallel. The power supply is 12V and each bulb has a resistance of 6Ω. The current flowing through one bulb is 2 Amps

calculate how much current the power supply delivers

2 x 3

= 6

A circuit contains 3 identical bulbs in parallel. An ammeter reads 250 mA for 3 minutes. Calculate the charge flowing through it during this time

250mA = 0.25 A

charge = current x time

0.25 x (3 x 60)

= 45C

A car has a p.d. of 12V across the terminals

How many joules are delivered per coulomb of charge?

12 J/C

Descibe how the resistance of an LDR varies with light intenisty

as light intensity increases, ther resistance decreases

Descibe how the resistance of a thermistor varies with temperture

as temperature increases, resistance decreases

Descibe how the resistance of a filament lamp varies with temperature

as a filament lamp gets hotter (higher temperature), resistance increasesas

Descibe how to calculate the resistance of a resistor from a graph

calculate the gradient

R = V ÷ I

R = 1 ÷ gradient

draw an I-V graph for a resistor

draw an I-V graph for a filament lamp

draw an I-V graph for a diode

What is 1 Volt equivalent to?

1 Volt = 1 Joules/Coulomb

What can lamps and LEDs be used to indicate?

the presence of a current in a circuit

LEDS emit light when current flows through them in a foward direction

Briefly: metal filament lamp on an I-V graph (explain resistance)

as the temperature of the meta filament increases, the resistance increases, hence the curve

Briefly: a wire on an I-V graph (expalin resistance)

the current through a wire (at constant temperature) is proportional to voltage

Briefly: different resistors on an I-V graph (expalin resistance)

the current through a resistor (at constat temperature) is proportional to voltage

different resistors have different resistances, hence the different slopes

Briefly: a diode on an I-V graph (expalin resistance)

current will only flow through a diode in one direction, as shown

If you increase the voltage you **increase/decrease** the current

If you increase the voltage you **increase **the current

What is the difference between alternation current (a.c.) and direct current (d.c.)? Give examples of each

mains electricity supply is a.c. meaning the current is constantly changing direction

cells and batteries supply is d.c. meaning that the current keeps flowing in the same direction

What are three uses of LEDs?

used for the numbers in digital clocks

in traffic lights

in remote controls

Do LEDs burn out? What light is this unlike?

unlike a light bulb, LEDs don't have a filament that can burn out

In a series circuit, what happens if you remove or disconnect one component?

In a series circuit, if you remove or disconnect one component then the circuit is brokena and they all stop

In a series circuit, the **same/different** current dlows through all parts of the circuit

In a series circuit, the **same** current dlows through all parts of the c

What does the total resistance of a ciruit depend on?

the total resistance of a circuit depends on the number of components and the type of component used

more components = more resistance

in parallel circuits each component is connected **separately/together **to the positive and negative power supply

if you remove or disconnect one component, it will **massively/hardly **affect the others

in parallel circuits each component is** **connected **separately **to the positive and negative power supply

if you remove or disconnect one component, it will **hardly **affect the others

Are parallel or series circuts used in your house? Why?

parallel

if you turn of one light you don't turn off all the lights

What happens when an electrical charge goes through a change in voltage?

when an electrical charge goes through a change in voltage, energy is transferred

energy is supplied to the charge at the power source to 'raise' it through a voltage

the charge gives up this energy when it 'falls' through any voltage drop in components elsewhere in the circuit

the bigger the change in voltage, the more energy is transferred for a given amount of charge passing through a circuit

A battery with a bigger voltage will supply **more/less** energy to the circuit for every coulomb of charge which flows round it

A battery with a bigger voltage will supply **more** energy to the circuit for every coulomb of charge which flows round it