Electricity Flashcards
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 1018 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
A1 = 0.18 Amps
what is the Amps of A2 and A3
why?
A2 = 0.18 Amps
A3 = 0.18 Amps
there s an equal amount of amps all aound the circuit
the current is consant
A1 = 0.34 Amps
what is the Amps of A2 and A3?
why?
A2 = 0.17 Amps
A3 = 0.17 Amps
the current is split in half
A2 + A3 = A1
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
V1 = 2.73 volts
V2 = 1.00 volts
what is V3 ?
why?
V3 = 1.73 volts
V2 + V3 = V1
what happens to V2 when you remove one of the bulbs?
the voltage increases
what happens to V2 when you remove a cell
the voltage decreases
V1 = 1.65 Volts
what are V2 and V3 ?
why?
V2 = 1.65 volts
V3 = 1.65 volts
they all have the same amount of volts
complete the data for all of the An knowing:
A3 = 2.5 Amps
A5 = 1.5 Amps
A6 = 2.0 Amps
A1 = 6.0 Amps
A2 = 6.0 Amps
A3 = 2.5 Amps
A4 = 3.5 Amps
A5 = 1.5 Amps
A6 = 2.0 Amps
A7 = 3.5 Amps
A8 = 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 1018 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 electricalenergy
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 V1 = 3.0 V what is V2, V3 and V4?
<span>V</span>2 = 3.0V
V3 = 3.0V
V4 = 3.0V
given that V2 = 1.5V, V3 = 1.5V and V4 = 1.5V, what is V1?
V1 = 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?
V1 = 4.5
V2, V3, V4 = 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 decreases- every other resistorincreases
what is the symbol for a diode?
if current flows <— then the diode …
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 Rh
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 (Rh) of the variable resistor?
V = I x R
R = V ÷ I
= 1.5 ÷ 2.25
= 0.6 Ω
the student wants only L3 to work
which switches should she close?
S1
S4
S5
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
