physics - electricity and Moments Flashcards
what are the units of charge, what is it measured in and what is it?
Q, measured in coulombs(C), and charge is a measure of how positive or negative something is
what are the units of current, what is it measured in and what is it?
I, measured in amps/amperes (A), THE RATE OF FLOW OF CHARGE - HOW MANY COULOMBS PASS A POINT PER SECOND
what are the units of potential difference, what is it measured in and what is it?
V, measured in volts (V), a measure of the energy transferred(work done) to or from each unit of charge between two points on a circuit
other definition of potential difference?
ho0w much energy a coulomb of charge gains/ loses between 2 points on a circuit
what are the units of resistance, what is it measured in and what is it?
R, measured in Ohms, a measure of how hard it is for electrons to move through a component
current and resistance are ? proportional
indirectly
what is the equation for charge (using current and time)
Q = It
Charge = current * time
what is the equation for potential difference (using current and resistance)?
V = IR
P.d = current * resistance
what is the equation for potential difference (using energy transferred and charge)
V = E/Q
P.d = energy/charge
what is the conventional current flow compared with the electron flow?
conventional current is when electric current flows from positive to negative around a circuit, whereas electron flow is when electric current flows from negative to positive as the electrons are repelling one another
What is Ohm’s law?
(for ohmic conductors), the current is directly proportional to the potential difference at a constant temperature
what does ohm’s law look like through an ohmic conductor (eg resistor)
a striaght line through the origin
what does ohm’s law look like through a semi-conductor diode?
a flat line along the x axis at 0 for the reverse bias and then an increase vertically from 0.8V onwards
what does ohm’s law look like through a light filament
a limit to proportionality on both the positive and negative axis : but goes through the origin and the current just stops increasing/decreasing
a diode only allows current to flow through in one direction true or false?
true!
current coming ? a junction is equal to the ? coming out of a junction
into, current
the current around a closed loop is always ?
constant
the potential difference across the power ? is equal to the sum of the ? difference across each of the ? - around a closed ?
supply, potential, components, loop/circuit
what is resistance?
a measure of how hard it is for electrons to move in an electrical circuit
Equation for resistance in parallel
1/RT = 1/R1 + 1/R2 +…
if the temperature in a circuit where a light comes on when the temp becomes too low, decreases - what happens to the resistance
it increases
what is a direct current and an example of it?
a current that always flows in the same direction, eg: cells/ batteries
what is alternating current? (and an example)
a current that is constantly changing, eg: mains electricity
what is the p.d. and frequency of mains electricity?
230V and 50Hz
what is the earth wire (function and colour)
it is for safety - so is at 0V - and stops any metal casing from becoming live. it only carries a current when a fault occurs. it is yellow and green
what is the neutral wire (function and colour)
it completes the circuit and carries away the current, remaining at ~0V, is blue
what is the live wire (function and colour)
provides the alternating p.d. from the mains supply ( ~230 ), brown wire
the brown ? wire is the worst to touch. your body (if ?) is at 0? so touching something at 230V creates a ? and causes a current to flow. if the path from ? to earth is a low resistance then a large ? can flow
live, earthed, V, p.d. , live, current
why is the brown live wire the worst to touch?
as it can complete the circuit and connect through you with the live wire
equation of energy including current, time and volts
E = ItV
3 main equations for power
P =E/t
P = IV
P = I(squared)R
what does the fuse do?
breaks the circuit if a fault in an appliance causes too much current to flow
what is static electricity caused by and what happens?
caused by friction, the electrons move from one electrical insulator to another
why does paper stick to a negatively charged rod?
the ? in the paper are repelled away from the ? (onto one ? of the paper) - making one side of the ? negatively ? and one side ? charged. the protons on the ? side will now be attracted to the ? as unlike/? charges ? - so the paper will ? to the rod
electrons, rod, side, paper, charged, positively, positive, rod, different, attract, stick
what is a static charge?
an electric charge that CANNOT move
what is the difference between an electrical conductor and an electrical insulator?
a conductor allows electrical charge to easily move through it, eg: iron or graphite, whereas an insulator does not allow electricity/electrical charge to move through it
what do electrically charged objects exert on other electrically charged objects?
a non-contact force
electrostatic charge is used in paint spraying:
the paint ? goes past a high voltage ? needle as it ? the spray, meaning the ? droplets spread out more. this is because they gain a ? charge so all ? one another meaning paint will cover the car more ?. the car body is ? charged so the paint ? are attracted to this - meaning less paint will be ? on the floor/walls of the ? shop
spray, positive, leaves, paint, positive, repel, evenly, negatively, droplets, lost/wasted, paint
insulators KEEP their charge - true or false?
true!
what is sparking?
when the static electric charge on an object becomes large enough meaning electrons can jump across the gap to an earthed conductor - creating a spark
examples of spaarking
when particles and water droplets in the air move past one another in clouds
where is an electric field created?
around any electrically charged object
what is an electric field and what is the charge at the centre
a region where a force acts on a charged particle, either a negative or positive charge
3 facts about electric fields:
- always drawn at ? angles to a ? object’s surface
- direction of ? shows which way the ? acts on a positive charge
- electric ? gets weaker as the distance from the charge ?
- right, charged
- lines, force
- field, increases
how is an electric field represented?
by field lines
Stronger the ?, the more field lines present and the ? the force felt
charge, stronger
why is electrostatic force non contact?
as it can be felt even when the objects aren’t touching
What is the “spark”
- The “?” is when the charge jumps through the ? from the highly ? object to the ? positive object, to ? out the charges
spark, air, negative, highly, balance
why do insulators stay charged?
as the electrons cannot move/flow
what does an electric field with one negative electric field and one positive electric field?
the negative has lots of arrows going towards the centre as they are attracted to the negative centre, while the positive has lots of arrows going out of the centre as they are repelled from the positive centre. there are also some arrows going from the positive to the negative.
what does an electric field with two positive electric fields?
arrows going out of both positives, as they are being repelled by the positive centres. however as they are both positive they bend away from each other at the centre between the tel positives instead of like with the positive and negative when the arrows go from positive to negative! x
Normally air is an electrical ?. When there is a very strong ? field the electrons in the air ? are removed from their nuclei (leaving a ? ion). These charged particles move in the electric ?. This is the spark.
insulator, electric, particles, positive, field
Equation for momentum
Momentum = mass times velocity
P = m*v
Equation for change in momentum ( and force)
F = change in p/ t
Force = change in momentum/time
Equation for a moment
Moment = distance times perpendicular force (from pivot)
Principle of a moment
(When an object is balanced) the clockwise moment = the anti-clockwise moment!!!!!
