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
