physics Flashcards
nano
10 to the power of -9
micro
10 to the power of -6
milli
10 to the power of -3
centi
10 to the power of -2
deci
10 to the power of -1
kilo
10 to the power of 3
mega
10 to the power of 6
giga
10 to the power of 9
insulators can be charged by
friction
charging is caused by
a gain or loss of electrons
like charges
repel
unlike charges
attract
applications of electrostatics
air cleaners
printers
photocopiers
hazards of electrostatics
electric shocks
fires or explosions
damage to electronics
role of earthing
The earthing protects the personnel from the shortcircuit current.
The earthing provides the easiest path to the flow of shortcircuit current even after the failure of the insulation.
The earthing protects the apparatus and personnel from the high voltage surges and lightning discharge.
alternating current
an electric current which periodically reverses direction and changes its magnitude continuously with time
direct current
direct current (DC) flows only in one direction.
current =
charge/time
resistance =
voltage/current
the total resistance ofa parallel combination is less than
that of any indiviualr resistor
voltage =
energy/charge
power =
current x voltage
difference between conductors and insulators
conductors let electric current pass through them
they possess very high electric conductivity
resistance of the flow of electric current is low
electrons can flow freely atom to atom
insulators do not allow electric current to pass trhough them
high electric resistane
electrons cannot move freely
example of a conductor
metal
example of an insulator
wood
voltmeter
measures electric potential in volts
ammeter
measures ac or dc in amps
negative temperature coefficent properties
If the device possesses negative temperature coefficient, it means the resistance of the device decreases with the increase in temperature.
thermistor properties
A thermistor (or thermal resistor) is defined as a type of resistor whose electrical resistance varies with changes in temperature. Although all resistors’ resistance will fluctuate slightly with temperature, a thermistor is particularly sensitive to temperature changes. used in thermostats, rechargable batteries, microwaves, fridges, ovens
LDR properties
DR’s are light-dependent devices whose resistance is decreased when light falls on them and that is increased in the dark. When a light dependent resistor is kept in dark, its resistance is very high.
ideal diodes properties
A diode is said to be an Ideal Diode when it is forward biased and acts as a perfect conductor, with zero voltage across it. Similarly, when the diode is reversed biased, it acts as a perfect insulator with zero current through it.
current rules for parallel circuits
the current in each branch after the split adds up to the same as the current just before the split.
voltage rules for parallel circuits
same everywhere
current rules for series circuits
same current everywhere
voltage rules for series circuits
sum of all indiviual voltages
Calculate the total resistance for resistor combinations in series.
sum of all indiivual resistacnes
the total resistance of a parallel combination is less than
that of any indiviualr resistor
energy transfer =
power × time
voltage applied to a series circuit is equal to the sum of …
indiviual resistances
a wire carrying a current in a magnetic field can experience
a force
F =
BIL
when a wire cuts magnetic field
lines, or when a magnetic field changes what happens
a voltage is induced
Vp/Vs =
np/ns
what does 100% efficiency lead to
total transfer of electrical power
VpIp =
VsIs
power transmission
`
speed =
distance/time
velocity =
change in displacement/time
acceleration =
change in velocity/time
v^2 - u^2 =
2as
types of force
weight, normal
contact, drag (including air resistance), friction, magnetic, electrostatic, thrust,
upthrust, lift and tension.
magnetic field patterna round a magnet
direction of a magnetic field pattern
north to south
soft magnetic materials
easily magnetised or demagnetised
hard magnetic materials
retain their magnetism after being magnetised
induced magnetism is
becomes a magnet only when placed in a magnetic field
what is the magnetic effect of a current
A straight current-carrying conductor has a magnetic field in the shape of concentric circles around it. Magnetic field lines can visualise the magnetic field of a straight current-carrying conductor.
The direction of a magnetic field produced due to a current-carrying conductor relies upon the same direction in which the current is flowing.
The direction of the magnetic field gets reversed if the direction of electric current changes.
g is
10 N 1/kg
w =
mg
what affects magnetic field strength around a wire
type of metal
amount of current
temperature of the wire
difference between permanent magnets and electromagnets
electromagnets can have a magnetic field when electric current flows through it and disappears when the flow of the current stops. On the other hand, permanent magnets are made up of magnetic material that is magnetised and has its own magnetic field. It will always display the magnetic behaviour.
work =
force x distance moved
what affects direction of a force on a wire in a magnetic field
If a current-carrying wire or other moving charge is placed in a stationary magnetic field it experiences a force due to the field produced by the moving charge and the stationary field. The direction of the force is perpendicularto the direction of movement and the stationary field lines. This is the principle behind an electric motor.
gravitational potential energy =
mgh (h is difference of height!)
construction of a dc motor
two bar magnets
a coil of wire wrapped around something to support it
an axle for the coil of wire to spin around
two half rings (‘split rings’)
The two bar magnets are held so that the north pole of one magnet faces the south pole of the other magnet. The coil of wire is mounted in the gap between the two magnets. The split rings make electrical contact with the coil and reverse the current every half turn. When an electric current flows through the coil, a force is exerted on the coil, causing it to spin.
operation of a dc motor
Electric motors use the forces produced by magnetic fields to produce a turning motion. If you put a length of wire in a magnetic field and pass a DC current through it (such as from a battery), the wire will move. This is called the motor effect.
factors affecting the magnitude of fforce produced in a dc motor
increasing the strength of the magnetic field
increasing the current flowing through the coil
thermal radiation is
electromagnetic waves in the infrared region.
what affects the magnitude of an induced voltage
number of turns
what affects the direction of an induced voltage
direction of movement. the current is reversed when the magnet is moved out of the coil
operation of an ac generator
A simple ac generator consists of a coil of wire rotating in a magnetic field
what factors affect the output voltage of an ac generator
number of turns (the more the more voltage is produced)
strength of magnetic field
rotational speed of rotor
output load on generator
graphical representation of the output voltage of a simple ac generator
applications of electromagnetic induction
magnetic stripe on credit card
old cd
step up transformer
the secondary voltage is higher than the primary voltage
step down transformer
the primary voltage is higher than the secondary voltage
number of turns on the primary and secondary coils
50 and 200
refletion causes
echoes
range of human hearing
20Hz to 20kHz
ultrasound uses
sonar and mecial scanning
power transmission
parts of the EM spectrum
(radio waves, microwaves, IR,
visible light, UV, X-rays, gamma
scalars have
magnitude
vectors have
direction and magnitude
distance vs displacement
displacement is the distance from the starting point, distance is total land covered
speed vs velocity
Speed is the rate of change of distance whereas velocity is the rate of change of displacement.
resultant force is
the force that alone produces the same acceleration as all those forces
elastic extension
Extension happens when an object increases in length, and compression happens when it decreases in length. The extension of an elastic object, such as a spring, is described by Hooke’s law: force = spring constant × extension
inelastic extension
when an object cannot stretch and return to its original shape
elastic limits
The elastic limit is the point at which applied stress causes an onset of permanent deformation and changes the slope of the stress-strain curve.
hookes law is
the displacement or size of the deformation is directly proportional to the deforming force or load. Under these conditions the object returns to its original shape and size upon removal of the load.
proportionality
This is a relationship between two quantities where they increase or decrease at the same rate. In other words, when quantity A changes by a certain factor, quantity B will change by the same factor.
inertia
a property of matter by which it continues in its existing state of rest or uniform motion in a straight line, unless that state is changed by an external force
what is free fall acceleration
When an object falls due to Earth’s gravitational pull, its velocity changes, and It accelerates due to the Earth’s gravity; it is said to be under the acceleration of free fall. This acceleration is calculated to be 9.8 m / s 2.
factors affecting air resistance
velocity
cross sectional area
shape and surface of the body
terminal velocity
the maximum velocity (speed) attainable by an object as it falls through a fluid. occurs when the sum of the drag force (Fd) and the buoyancy is equal to the downward force of gravity (FG) acting on the object.
forces invovled in terminal velocity
drag = downward force of gravity
law of conservation of momentum
when a system of interacting objects is not influenced by outside forces like friction then the total momentum of the system cannot change. In other words, the total momentum of a system of objects remains constant during any interaction if no external force acts on the system.
useful energy
The portion of final energy which is actually available after final conversion to the consumer for the respective use.
wasted energy
not usefully ttransferred or transformed
effect of temperature on density of fluid
when temperature increases, with pressure constant, density decreases. Density is affected by temperature because as temperature increases so does the kinetic energy of the particles.
factors affecting rate of absorption and emission of thermal radiation
increase:
motor effect
the coil of wire has an electrical current running through it because it is connected to the cell
this generates a magnetic field around the wire
the current is turned on and off at the correct time so the magnetic field of the wire interacts with that of the two magnets
this makes the coil rotate
factors affecting rate of absorption and emission of thermal radiation
dull surface and darkdecreases shiny surface and white
effect of pressure on gas volume
increase of pressure, decreased volume of gas
effect of temperature on gas volume
When the gas is heated, its volume increases. The particles gain kinetic energy and move faster. They collide more often with greater force on the container walls. Since the container can expand, the gas volume increases until the pressure of the gas is back to the constant atmospheric pressure.
melting point
the temperature at which it changes state from solid to liquid
boiling point
The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor.
latent heat of fusion
the amount of energy that must be supplied to a solid substance (typically in the form of heat) in order to trigger a change in its state
latent heat of vaporisation
heat required to convert a unit mass of a liquid into vapor without a change in temperature
compare densities of solids liquids and gases
Put simply, solid masses have a high density as particles are very close together, liquid masses are slightly less dense, and gas masses have a very low density with particles much further apart.
transverse waves
a wave in which the medium vibrates at right angles to the direction of its propagation.
longitudinal waves
a wave vibrating in the direction of propagation.
peak
the highest point above the rest position
trough
the lowest point below the rest position
compression
high density wave period
rareefraction
low density wave period
amplitude
the maximum displacement of a point of a wave from its rest position
wavelength
distance covered by a full cycle of the wave, usually measured from peak to peak, or trough to trough
frequency
the number of waves passing a point each second
period
the time taken for a full cycle of the wave, usually measured from peak to peak, or trough to trough
reflection at a surface
Reflection from a smooth, flat surface is called specular reflection. This is the type of reflection that happens with a flat mirror. The image in a mirror is:
upright
virtual
In a virtual image, the rays appear to diverge from behind the mirror, so the image appears to come from behind the mirror.
refraction at a boundary
The density of a material affects the speed that a wave will be transmitted through it. In general, the denser the transparent material, the more slowly light travels through it.
Glass is denser than air, so a light ray passing from air into glass slows down. If the ray meets the boundary at an angle to the normal, it bends towards the normal.
The reverse is also true. A light ray speeds up as it passes from glass into air, and bends away from the normal by the same angle.
effect of reflection and refraction on the speed
slows as it enters glass (and so wavelength decrease)
effect of reflection and refraction on the
frequency
if the wave slows down, its frequency remains the same, due to the fact that its wavelength is shorter.
effect of reflection and refraction on the wavelength
So if a wave slows down, its wavelength will decrease.
effect of reflection and refraction on the direction of waves.
changes direction due to one side of the wave changing speed before the other
reflection and refraction of light with water waves
water changes direction in water as its denser
doppler effect
an increase (or decrease) in the frequency of sound, light, or other waves as the source and observer move towards (or away from) each other. The effect causes the sudden change in pitch noticeable in a passing siren, as well as the red shift seen by astronomers.
production of soudn waves
This vibration produces waves in the medium that oscillates the membrane of our ears and hence we can hear sound.
need for a medium
sound waves but not EM waves
the higher the ampltiude the what the noise
louder the sound
the lower the amplitude the what the noise
quieter the sound
the higher the pitch the what the frequency
the higher the sound
the lower the pitch the what the frequency
the lower the sound
distinction of the component parts by different wavelengths
and/or frequencies.
radio
micro
infrared
visible
ultraviolet
x rays
gamma rays
the order of the component parts by wavelength and/or frequency.
radio - low energy low frequency long wavelength
micro
infrared
visible
ultraviolet
x rays
gamma rays - high energy high freq short wavelength
applications and hazards of the component parts of the
electromagnetic spectrum
radio - radio
micro - satellites
infrared - remote controls
visible - seeing
ultraviolet - sun tan lamp
x rays - imaging
gamma rays - medical tracers
atomic number
no of protons = no of electrons
mass number
no of neutrons + protons
isotope is
different no of neutrons
nuclide is
a distinct kind of atom or nucleus characterized by a specific number of protons and neutrons.
nuclide notation
top: mass number A
bottom: atomic number Z
emissions arise from
an unstable nucleus
differences between alpha, beta and gamma emission
alpha: helium nucleus
positively charged
low penetrating ability
more ionizing power
beta: electron or positron
positively or negatively charged
moderate penetrating ability
less ionising power
gamma: photon carrying EM energy
no charge
high penetrating ability
very small ionising power
effect of decay on atomic number
alpha: atomic number decreases by 2
beta: incraeses by 1
gamma: none
effect of decay on mass number
alpha: decreases by four
beta: sam
gamma: no change
penetrating abilities of alpha, beta and gamma radiation.
increases
e relative ionising abilities of alpha, beta and gamma radiation.
decreases
deflection of alpha, beta and gamma radiation in
electric or magnetic fields.
alpha and beta
not gamma
f background radiation.
a measure of the level of ionizing radiation present in the environment at a particular location which is not due to deliberate introduction of radiation sources. Background radiation originates from a variety of sources, both natural and artificial. These include both cosmic radiation and environmental radioactivity from naturally occurring radioactive materials (such as radon and radium), as well as man-made medical X-rays, fallout from nuclear weapons testing and nuclear accidents.
applications and hazards of ionising radiation
medicine, industry, agriculture and research
health hazards liek cancer
half life
the time required for a quantity to reduce to half of its initial value
angle of incidence =
angle of reflection
what is diffuse reflection
If a surface is rough, diffuse reflection happens. Instead of forming an image, the reflected light is scattered in all directions. This may cause a distorted image of the object, as occurs with rippling water, or no image at all. Each individual reflection still obeys the law of reflection, but the different parts of the rough surface are at different angles.
which objects emit IR
ALL of them
if an object falls, its speed is ________ and acceleration is ________
speed is increasing as acceleration is constant
A decrease in temperature does what to the flow of current at a given potential difference in a filament lamp.
increases the flow of current at a given potential difference in a filament lamp.
in bright light, what happens to a LDR
the resistance of the LDR is low and more current can flow through it. This can be rationalised by considering Ohm’s Law which states that V= IR From this it is clear to see that resistance and current are inversely proportional and hence as the resistance decreases, the current increases.
charge
measured in couloumbs
Q
1 coulomb is defined as
the amount of charge that passes in 1 second when the current is 1 ampere
a current of 1A means that 1
coulomb of charge flows past that point every second
1V means that
1 joule of work is done in pushing 1 coulomb of charge through a particular area/component.
power
ratae of transfer of energy
1W is
the transfer of 1 joule of energy per second
resistors in parallel
total resistance of the parallel combination is less than the resistance of any individual resistor
resistors in parallel equation
Rt = R1/n
charge prefers the path
of least resistance
what is a short circuit
the charge bypasses the component by taking the path of least resistance
which way is the diode placed
in forward bias (the arrow points in direction of the current) unless it is designed to be in reverse bias
what is an ideal diode
one that is a perfect conductor one way and a perfect insulator the other
what happens if a diode is in reverse bais
no charge can get through it (so circuit breaks)
current flows..
from postitive to negative
what is a transformer
a device that changes voltage and current, whilst keeping power the same.
what transformers are used in the national grid
step up transformers
why are low currents helpful
a higher current means more energy is lost as heat
what current do transformers require
alternating current and not direct current
electromagnetic induction is essentially
making electricity by moving a magnet in a coil of wire
creating a potential difference
moving the magnet inside a coil one way
generates a positive voltage whilst the other way would generate a negative voltage
what happens if you keep moving the magnet backwards and forwards through the coil (or spin it)
you create a potential difference that keeps on changing direction (alternating current)
factors influencing the size of the induced voltage
The speed of rotation of the magnet (or coil)
The size of the magnetic field
Having more turns of wire on the coil
The area of the coil
how do you increase a current in an AC generator
Increase the speed of rotation
Increase the strength of the magnet
Increase the number of turns of the coil
Increase the area of the coil
Keep the coil perpendicular to the magnetic field
flemings right hand rule
The ThuMb shows the direction of Motion.
The First Finger shows the direction of the Field.
The SeCond finger shows the direction of the Current.
When you rub two of these insulators together, electrons can get transferred between them. So
one of the items loses electrons (and becomes positively charged), and the other one gains electrons (and becomes negatively charged). Which way the electrons are transferred depends on the materials.
dangers of static electricity
when there’s a spark of static electricity in an area where there’s a buildup of flammable fumes (eg: power plants, petrol stations etc). We get around this by earthing objects - ie: connecting them to the ground using an electrical conductor. That way, static electricity won’t be an issue because charge would never build up on the item. Instead, it would flow through the conductor and be absorbed by the ground.
uses of static electricity
pollution control to attract dust particles
printing
spray painting
why are capacitors suitable for use in defibrillators
Capacitors can store electrical charge. The amount of charge stored and the rate of release can be varied. The defibrillator circuit can release a variable amount of charge based on the size of the patient. The charge in the capacitor is released very quickly in a short burst.
Virtual Image
an image which appears to be formed from rays of light, but in reality is not formed.
focal point
the point of a lens where light rays appear to diverge from or converge to.
what should you remember about beta particle emissions
a neutron is converted int o a proton
What basic principle enables electric motors to operate?
A closed-loop conductor within a changing magnetic field will have an induced electromotive force.
is the freq of ultrasound higher or lower than human hearing
higher
waht can ultrasound be used for
medical imaging
sonar location
what connects the lungs to the back of the mouth
the trachea
what is ohms law
V=IR
Ohm’s law states that the voltage across a conductor is directly proportional to the current across the component provided all physical conditions, such as temperature, remain constant. The graph of an ohmic conductor has a positive gradient.
what is Heterosis
(hybrid power, hybrid strength) is the superiority of first-generation hybrids over their parent forms in terms of viability, yield, fertility and a number of other characteristics. To obtain the effect of hybrid power, it is important to choose unrelated forms representing different lines, breeds, even species as parents.
what is the tidal volume
basically the normal breathing cycle or the amount of air breathed in or out in one cycle. If you are sitting down normally and breathing in 1L of air and then breathing out 1L of air, 1L is your tidal volume.
