P3.1 Flashcards
How do you produce static electricity?
How is what object becomes charges decide?
How do you discharge an object, and what are sparks?
W1) when you run two materials with each other, electrons are transferred from one to another. If these are conductors, the electrons will just flow back and keep a neutral charge but if they are Insulators- electrons can!r flow, and so one will be negative and one positive.
This charge an insulator gains is called STATIC ELECTRICITY.
2) which object becomes positive and which one becomes negative is decided by the material
- an acetate rod loses electrons
- but a polythene rod gains electrons from a duster
3) you discharge an object by touching it with a conductor, sparks also discharge charged objects like a van de Graf generator, or also clouds with the floor. SPARKS are flow of CURRENT THROUGH THE AIR.
Gold leaf experiment
Touch a charged insulator to the zinc plate, say negative, then all the electrons will flow inside. The stem and the gold leaf will have the same charge, and repel, each other, making the gold leaf stand. Similarly if the insulator is positively charged, the electrons from the stem and leaf will go into the insulator, making the leaf and stem both positively charged and again repelling each other, making it stand.
How does a ballon stick to the wall (induces)
This works for all charged and neutral objects…
A balloon has just been electrically charged, and when placed ends a neutral object, like the wall, the ELECTRONS ONLY either attract or repel from the surface, inducing the surface in the object. The two objects can now attract…
Works with ballon paper and water too…
How does van de Graf generator work
How does lightning work
1) as belt moves up and down, it gains electrons from the other insulator in the dome, leaving the dome positively charged.
2) if you put your hands on it, you become positively charged too, and all your hair are all positively charged, therefore they repel each other and stand up.
3) when done, you discharge yourself by touching discharge reconnected to earth, which allows for electrons to flow back.
Similarly a thundercloud becomes negatively charged, then the ground will becomes positively charged. If enough charge is built up, electrons move through the air to the ground I. The form of lightning.
Field lines and electric fields
How are positive and negative different
How they work and what happens if two interact
Also what about distances ?
What does a direction for field line show?
Electric charges each have their own electric field, like mass in gravity, where a charged particle will feel a force if placed into it.
It can be shown using field lines, the closer the field lines, the stronger the field. Positive charged spheres are OUTWARDS, negative INWARDS
If w charged particle is placed in an electric field, an electrostatic force is produced.
1) if the field lines are in same direction, then it will join up, and be attracted to each other
2) if filed lines opposite direction, then field lines will push against each other, and repel
3) the closer the field lines the stringer the strength of electrostatic force
4) directions shows the direction of force on a positive charge
Charge formula =
What is current
What is PD
When will current only flow?
Charge (C) = Current (A) x Time(s)
Current (I) is the rate of flow of charge (which is electrons), so how fast electrons move
PD is the driving force of the charge (electrons), in volts
The Positive terminal here has a higher electrical potential then negative, and this difference is pd
2) when there is a pd and the circuit is closed!
Remember the symbols for components ina circuit
Battery is two cells with dotted line
Diode is circle with triangle and a vertical line touching it
LED is diode with two arrows on top right pointing top right
Resistor rectangle
Variable resistier rectangle with arrow top right through it
LDR is circle with rectangle with two arrows top left pointing bottom left
Thermistor is rectangle with line through it and small line at the bottom
Energy equation for charge and PD
Energy transferred (J) = charge (C) X PD ( )
Potential difference is the Energy being transferred per unit of charge (how much energy an electron takes to go) and transfer this to say a motor
What happens to current and volt in series circuits, how do you measure both things
Current is the same everywhere, so you can measure it anywhere with an ammeter too in SERIES
Volts are split among the components . To measure it, join a voltmeter in PARALLEL
What happens to current and volts in parallel circuits
1) Pd is the same in all different branches, but then it gets treated like a series and splits amongst those components. It is the same because each charge pass down one branch and transfers all the energy…
2) current split between branches. Current in each branch is equal to v/r,, the voltage / by the total resistance in that branch.
Just remember everything in = everything out
What happens to total resistance in parallel and series?
Series=
- total resistance is = to sum of all resistance in components/ resistors
Parallel=
- total resistance will always be less then the resistance of each resistor or component, basically lower then the lowest resistance. This is because of the way the current splits.
A circuit in series will always have more resistance then circuits with same resistors in parallel…
Equation connecting voltage current and resistance
What is the relationship between resistance and current
Voltage (V) = current (A) x resistance (ohms)
Current and resistance are inversely proportional, increase resistance, decrease current
How to go about investigating resistance…
1) connect ammeter in series’s
2) voltmeter in parallel
3) connect a variable resistor before the ammeter in series too.
4) vary the resistance of the variable resistor. This will give different currents and PDs across the component you are testing, such as a filament lamp or a fixed resistor or a diode. Then you can plot I /V graphs
5) for thermistor you should use different temps like putting it in water and heating it up
6) change light intensities for the LDR
Fixed resistor/ wire and it’s I/V characteristic graph
What must we assume stays the same when current is increased in this
Also what is the BOTTOM left Quadrat show
A graph of I/V , is straight through the origin, and current is directly proportional to voltage. Different resistors have different p.ds but if it goes through origin it is a fixed/ variable resistor.
Must assume temp stays the same
This happens because the resistance is fixed (if temp is 0) so the gradient stays the same
It still shows the linear relationship, but just what happens if the current went the other way.
What is ohms law
What resistor obeys it
Current through a component will be directly proportional to its voltage provided the temp stays constant
Wires and the fixed resistor
What about resistance ina filament
Lamp?
Why does it go up but then level off and resistance increases a lot?
When current increases, what increases?
I/ V characteristic graph is not linear and does not obey ohms law
1) graph rises steeply, then levels off. This happens because initially the resistance of the graph is low, and this is because the TEMPERATURE IS LOW. When Temperatur is low , kinetic energy of particles in resistor are low too, and they don’t vibrate much. But when they are hot, the ions in the resistor vibrate more, and collide with the delocalised electrons more, acting as an impede net to electron flow, and therefore increasing the resistance,
- as the current increases, the temp does too and the resistance then increases a lot- making the graph curved. Resistance starts off low then a lot- there is a limit too how much current you can put into things before the resistance becomes too high and current actually decreases
What about resistance in diode, and what is a diode?
DIODES ARE COMPONENTS THAT ONLY LET s CURRENT GO ON ONE DIRECTION. This means only in the direction the arrow is facing.
1) on one direction, the diode allows current too pass, and the resistance is similar to a fixed resistier graph- not completely directly proportional but close
2) if you revers the voltage direction there will be no current let through. Resistance is also 0
What is a thermistor and what does resistance do with it. Also why do they use a semis conductor of silicon?
Where find them
A thermistor is a resistor that it’s resistance depends on temperature.
1) thermistors are made up of SEMICONDUCTING MATERIAL LIKE SILICON. With these materials, it doesn’t take a lot of energy for electrons to escape the atom and form current.
2) this means, that with an increase of temperature, the thermal energy will transfer to the electrons and they will easily form current. High temps= high current
3) at a certain pd, high current= low resistance, low current= high resistance.
4) therefore in thermistors the higher the temperature, the Lower the resistance,
5: it’s I/V graph will be like increasing acceleration = curved up ad increase of temp makes a lower resistance.
6) finally we use thermistors in things like thermostats, irons, etc, ovens and stop tablet from overheating
What about LDRs? How do they work and how does resistance vary with it?
LDRs resistance is dependent on their light.
1) basically same as thermistor. They are also made of SEMI CONDUCTING MATERIAL LIKE SILICON. this time it is sensitive to light, and increase of light allows electrons to be released from the atoms into the circuit to increase current
2) increase light= increase current= decrease resistance, and vice Verca
3) I/v graph and resistance against condition graph (light/ temp) exactly the same as a thermistor…
4) good for automatic night lights and stuff , burglar detectors etc.
4) it looks like a rectangle in a circle with two arrows pointing bottom left from top right. Remember it.
Finally how can LDRs and thermistors be used in sensing circuits
So if a fan is done extend, then as the temp increases, the resistance of the thermistors decreases, meaning it takes a lower share of voltage and shares more with the other fixed resistor and fan in parallel. Since the fan is in parallel, it will receive the same voltage as the fixed resistor (and this overall higher now) so the fan will increase speed.
For LDR, resistor, then LDR and a bulb connected in parallel. What happens is when light is lowest , the resistance is the highest. This means more of the voltage is taken by this resistor, and since in parallel, also taken by the bulb, making it more bright…
Not needed to know but useful
What is a 0 error and what is the consequences of having one
zero error is if the analogue meter on the reading display is not set to zero before you do measurements, readings won’t go through origin. Make sure to check this.
Equation for power in electricity (same thing otherwise) with energy and time
Power (W) = energy (J) / time( s)
Energy therefore = power x time
Energy can be in joules are KWH, in this case jus convert power to kilowatts and time into seconds easy
Equation for power with current and pd
Also with resistance
Also with charge
Power (W)= pd (V) x current (A)
We know pd = IR
Then power also = I2R
Power = energy/t
Remember that energy= charge (C) x pd( V) too
