P3 Flashcards
How do object become charged?
Transferring electrons, with the force of friction
What are fields?
A region within which object experience a force
What is essential for the three fields?
Gravitational = needs mass
Magnetic = needs anything with magnetic properties
Electric = needs a charged object
What way do electric field lines go?
(electrostatic)
Leave positive and enter negative
Positive is the long wire, negative is the short
What do charge objects experience in an electric field?
Repulsion or attraction
What is current?
The rate of flow of charge, how many electrons pass a point in a second
What is the formula for current?
I = Q➗ T
I= amps
Q= coulombs
T= seconds
What is the symbol for a diode?
A circle with a triangle , line at the end pointing in the direction of current
What is the symbol for an LEd
The symbol of a diode with two arrows coming out of the circle
What is the symbol for a fixed resistor?
A solid rectangle
What is the symbol for a variable resistor, what does it do?
A solid rectangle with an arrow going diagonally though
Vary the resistance, and the current and p.d
What is the symbol of a fuse?
A rectangle with a line going through
What is the symbol for a heater?
A solid rectangle cut into boxes
How much charge does an electron carry?
1.6 ✖️10^-19 coulombs
What is voltage?
The measure of energy per charge
V= E/ Q
What is potential difference?
Difference in voltage between two points
What is the equation for potential difference? (Energy)
V = W➗Q
V= potential difference ,v
W= work done, J
Q= charge , C
What is resistance?
The opposition to the passage of charge (current)
How does temperature affect resistance?
The more kinetic energy the positive ions have the more they vibrate up and down. Stopping them flow, reducing current.
The greater the temperature, the greater resistance
Why does current transfer energy in a circuit?
Resistance, the higher the resistance, the more energy is transferred by the current
What is the main equation for potential difference?
V=I ✖️R
V= pd, volts
I= current , amps
R= resistance, ohms
What is charge?
A property of matter ,
Electrons carry charge
What is a series circuit?
The electrons must travel through every component,
Just one loop, no branches
How does the current differ in a series circuit?
It stays the same throughout
It=I1=I2
How does the voltage differ in a series circuit?
The total voltage is shared throughout the circuit
Vt=V1+V2
How does resistance differ in a series circuit?
It’s shared out throughout the circuit
Rt=R1+R2
What is a parallel circuit ?
The electrons do not travel through the same components.
The circuit has branches
How does current differ in a parallel circuit?
It distributed between each branch
It= I1+I2
How does potential difference differ in a parallel circuit?
It is the same across each branch
Vt = V1 =V2
How does resistance differ in a parallel circuit?
1/Rt= 1/R1 + 1/R2
What p.d is required to create 1A?
100 kw
Therefore it is very unlikely that you’d be injured by an electrical currents
What is the gradient of an I-V graph ?
1/R
Opposite of resistance
What is ohms law?
The current through a component is directly proportional to the potential difference, as along as the temperature is kept constant
What does a diagonal straight line show on an IV graph?
Constant resistance
What does a steep gradient show on an IV graph?
low
resistance
What does a shallow gradient show on an IV graph?
high resistance
Explain why as the p.d increases , the component gets hotter?
Some of energy transferred as the electrons pass through the component (voltage).
more energy transferred per coulomb of charge
Some of this energy is transferred to heat
What pattern do fixed resistors follow on an IV graph
🔺Diagonal straight line (linear circuit element) - resistance is constantly
🔺Ohmic conductors (follows Ohm’s law)
How can you note temperature in an IV graph
As the p.d is increasing, so is the temperature
Describe the IV graph for a filament light bulb
🔺The resistance increases with p.d
🔺As the resistance increases as it is getting hotter
🔺Non - linear circuit element
Describe the IV graph for a diode
Forwards resistance is low
Reverse resistance is high
How does the net resistance change when you add more resistors in a series circuit?
The net resistance increases as the total current decreases
How does the net resistance of a parallel circuit change when you add more resistors?
The net resistance decreases, and will always be smaller than the resistance of the smallest resistance branch
The total current increases
What is a sensor circuit?
A circuit that turns a component on or off automatically in response to external stimuli
What is a thermistor?
A type of resistor who’s resistance in reduced greatly by heating
Inverse temp and resistance
Describe how a thermistor works
🔘in series with a fixed resistor and in parallel with a component
🔘as temperature decreases, resistance increases (more than the fixed resistor)
🔘as ratio of shared resistance increases so does the shared p.d
🔘as in parallel with the component the p.d also increases at it is the same
🔘once voltage is high enough the working potential is reached and it is switched on
How would you calculate sensor circuits
Use ratios and assume the same ratio for P.d as resistance ratios
What is electrical power?
The rate of electrical energy transfer
Joules per second
What is the formula for electrical power?
P=I ✖️V
P=Watts
I= amps
V= volts
What is the equation for electrical power(2) ?
P = I^2✖️R
P= watts
I= amphs
R=ohms
What are watts a measures of?
The amount of joules transferred in a second
What is a diode?
A semi- conduct that allows current to flow easily in one direction, but restricts it in the other
What is an LDR ?
A light dependant resistor.
When the light intensity decreases, the resistance increases.
Why does moisture decrease the build up of static charge?
Moisture can conduct charge, not allowing it to build up
How does the amount of resistance wire affect the current?
The more the wire , the less the current
The less wire, the more current
How is the relationship between temperature and p.d shown on a graph?
A curving gradient of resistance as p.d increases
How is current calculated?
if given a certain amount of electrons
The number of electrons ✖️1.6*10^-19 coulombs
What happens to the electrons when the current is doubled?
The amount of electrons present doubles
What do the electrons look like in a wire with no current?
Electrons are present , but all are moving in random directions. They all chance, each other out with an overall 0 charge.
How do thermistors decrease their resistance with increased temperature?
The ions vibrating faster < temperature releasing electrons from their shells- decreasing the resistance
Why are their differences in voltage between the wires?
The cell/ battery creates chemical reactions which bunch up the electrons in places of the wire. So the electrons will travel from a high point to a low point , creating a p.d
Why do the electrons travel from high voltage to low voltage?
Everything wants to have a lower energy state in the world.
describe the relationship between current and resistance
describe the relationship between temperature and resistance
Mention how it impacts current
what are the conditions needs for charge to flow?
- a source of potential difference
- a closed circuit
what does it mean to be neutral?
a zero net charge, an equal amount of positive chanrge as negative charge
how do you produce static electricity?
rubbing 2 insulators together transfering electrons from onr to the other creating a positive and neative charge
what is discharge?
(removing the charge)
connecting to something that allows charge to flow
like a metal
air can conduct electricity
what are sparks?
a flow of charge or current through the air
define current :
the rate of flow of charge (electrons)
what are the conditions required for charge flow?
- a closed circuit
- source of potential difference
compare series and parallel circiuts
- in parallel if one branch/ component breaks don- then the rest of the circuit remains unaffected
how do you measure current in series ?
place the ammeter anywhere within the circuit in series, it will have the same reading all around because current is the same in a series circuit
how do you measure current in a parallel circuit?
since current is shared throughout each branch , place the ammeter in series for each branch and the total wll be the total current
how do you measure potential difference in a series circuit ?
place the voltmeter in parallel (wire with both sides of the component )
how do you connect an ammeter ?
Negative terminal next to negative terminal
How do you measure the potential difference in parallel?
the voltmeter in parallel to the cell will be the same as the pd for each branch
How do you get the lowest total resistance ?
(in parallel circuits)
The more components in parallel, the less Total resistance
What side of the cell is negative and positive?
Why would you use a resistor or a resistance wire ?
If you want the resistance to be constant
What Is resistance ?
The collision of electrons with metal ions
What is a linear circuit element ?
Resistance doesn’t change as the potential difference changes (constant resistance)
How do thermistors decrease their resistance as temperature increases?
The semi conductor material allows electrons to escape from the atoms , producing current
What happens when you add components to a series and parallel circuit?
Where will there be more current (in a circuit) ?
Where less resistance is offered (less components)
