spec Flashcards
what is the difference between AC and DC
AC is constantly changing magnitude and direction. AC is how mains electricity is produced from turbines.
DC is constant and is produced from a battery and used in some sensitive components like in computing.
watt happens when you increase the voltage
As voltage increases the current also increases.
what happens when you have more components in a circuit
In general, the more components in a circuit, the lower the current.
what would the graph look like with an ohmic resistor, a filament lamp and a diode
a straight like, an “S’, a horisontal line and up
what happens when you increase the resistance in a circuit
Since V = IR, as you increase the resistance in a circuit, the current will decrease
electric current in solid metallic conductors is…
a flow of negatively charged electrons
to calculate total voltage in a series circuit
V1 +V2 +V3…
to calculate total resistance in a series circuit
R1 + R2 + R3…
total current in a series circuit
I1 = I2 = I3
Wavefront
Created by overlapping lots of different waves. The wavefront is the front of the wave, or the same point on each wave
Amplitude
The maximum displacement of particles from their equilibrium position.
Wavelength
The distance between a particular point on one cycle of the wave and the same point on the next cycle.
Frequency
The number of waves passing a particular point per second. Is measured in Hertz (Hz).
Time Period
The time it takes for one complete wave to pass a particular point.
electromagnetic spectrum
radio, microwave, infrared, visible, ultraviolet, x-ray and gamma ray radiations
how does the speed differ for the waves in the electromagnetic spectrum in free space
all these waves travel at the same speed in free space
electromagnetic spectrum from biggest wave length to smallest wave length
radio, microwave, infrared, visible, ultraviolet, x-ray, gamma ray radiations
electromagnetic spectrum from biggest frequency to smallest frequency
gamma ray radiations, x-ray, ultraviolet, visible, infrared, microwave, radio
visible light, from lowest to highest frequency
Red, orange, yellow, green, blue, indigo, violet
use of radio waves
broadcasting and communications
use of microwaves
cooking and satellite transmissions
use of infrared
heaters and night vision equipment
use of visible light
optical fibres and photography
use of ultraviolet
fluorescent lamps
use of x rays
observing the internal structure of objects and materials, including for medical applications
use of gamma rays
sterilising food and medical equipment
effects of microwaves
internal heating of body tissue
effects of infrared
skin burns
effects of ultraviolet
damage to surface cells and blindness
effects of gamma rays
cancer, mutation
protection from UV
- sun glasses
- sun cream
- stay in shade
protection from gamma rays
Wear led clothing
investigate the refraction of light, using rectangular blocks / semicircular blocks / triangular prisms
- draw outline of block
- Draw the normal
- Draw a line at 30 degrees to the normal, and shine a ray of light on the line
- Draw a line where the light emerges on the other side (emergent ray) and connect the two lines
- Measure the angle of the emergent ray
what happens to refraction as a medium becomes more dense
light bends towards the normal, because the light rays in the denser medium move slower
total internal refraction in optical fibres
You send the light in at an angle that is more than the critical angle of the internal core material, so it totally internally reflects.
Optical fibres are not bent much to ensure that it always hits the core at more than the critical angle.
how is total internal reflection useful in optical fibres
Optical fibres are used to transmit information. Total internal reflection is very useful in optical fibres as no information is lost
what are optical fibres made from
glass , plastic
what stops total internal reflection in optical fibres
This total internal reflection will only not occur if the optical fibre is bent too sharply.
total internal refraction in prisms (e.g. periscopes)
white light is shone through the triangular prisms. White light is in the very middle of the EM spectrum, so is a combination of all the waves, from red to violet. Therefore, when shone into a prism, each part refracts different amounts, so they separate into their colour when they leave the prism.
explain what is meant by critical angle
- The angle of incidence which produces an angle of refraction of 90
- When the angle of incidence is greater than the critical angle, total internal reflection occurs
- This effect only occurs at a boundary from a high refractive index material to a low refractive index material.
energy stores
chemical, kinetic, gravitational, elastic, thermal, magnetic, electrostatic, nuclear
energy transfers
mechanically, electrically, by heating, by radiation (light and sound)
the principle of conservation of energy
In any process energy is never created or destroyed. (It is just transferred from one store to another.)
what is work done equal to
energy transfered
relationship between GPE and kinetic energy for a falling object
Because energy is conserved,
the decrease in GPE = increase in KE, for a falling object if no energy is lost to the surroundings
what is power?
rate of work done.
p = E/t
pressure in liquids and gas
Pressure in gases and liquids (at rest) act equally in all directions.
what happens when the same force is applied over a larger area
If the same force is applied over a larger area, there will be a lower pressure
what happens the the thermal and kinetic energy of particles at absolute zero
At absolute zero the particles have no thermal energy or kinetic energy, so they cannot exert a force.
absolute zero
0 Kelvin = -273˚C
rhyme to remember how to convert kelvin to celcius
K is equal to degrees C plus 273
relationship between kelvin temperature and kinetic energy
The Kelvin temperature of a gas is proportional to the average kinetic energy of its molecules.
feild line practical
- draw around bar magnet
- Place a compass at one pole
- Draw a ‘dot’ to show there the compass is pointing,
- Move the compass so the opposite end of the needle is pointing to the dot,
- Repeat steps 3 and 4 until to reach the other pole of the magnet.
- Do this procedure at least 5 times from different points on the pole of the magnet.
- Join up your dots to create the field line plots
what is a uniform magnetic feild?
A uniform magnetic field is comprised of straight, parallel lines which are evenly spaced. Between two opposite charges on flat magnets, a uniform magnetic field is formed.
how to make a uniform magnetic field with permanent bar magnets
If you put two opposite poles close to each other, they will attract and make a uniform magnetic field.
The closer together, the stronger the magnetic field.
what happens when an electric current flows in a conductor
produces a magnetic field around it
how does a d.c electric motor work
- Current flows in the wire/coil.
- This creates a magnetic field around the wire/coil.
- This magnetic field interacts with the field from the permanent magnet.
- This produces a force on the wire/coil which moves the wire/coil.
- The split-ring commutator changes the direction of the current every half turn as it spins. This reverses the direction of the forces, allowing the coil to continue spinning.
how does a loudspeaker work?
- An alternating current from the source passes though the coils in the speaker.
- This current is constantly changing direction and magnitude
- This current creates a magnetic field around the coil
- This field interacts with the magnetic field from the permanent magnets
- Creating a constantly changing force on the coil.
- This causes the coil to vibrate in and out as the direction of the force changes, moving the cone
- The cone causes vibrations which we hear as sound waves.
atomic number
the number of protons in an atom
mass number
protons + neutrons
when do we mean when we say that a material is “radioactive”
it consists of unstable isotopes that can decay
what chemical symbol do we normally represent alpha (α) radiation with
He
(helium, as it has 2 protons and 2 neutrons)
charge of alpha (α) radiation
2+
(as it doesn’t have any electrons)
what can alpha particles be absorbed by?
a single sheet of paper (their particles are fairly large so they don’t penetrate far)
how ionising are alpha (α) particles?
strongly ionising (meaning they can easily knock electrons off of any atoms they collide with)
charge of a beta particle
-1 (as it is an electron)
what can beta particles be absorbed by?
5mm of aluminium (they penetrate moderatley far)
how ionising are beta particles?
moderatley ionising
if gamma rays are not particles, then what are they?
waves of electromagnetic radiation
how ionising are gamma rays?
weakly ionising (as they have no mass or charge and so pass through materials)
what can gamma rays be absorbed by?
thick sheets of lead or multiple layers of concrete (as they penetrate really far)
what is ionisation?
when an atom loses or gains an electron, causing it to become an ion (an atom which is positively or negatively charged).
explain how alpha beta and gamma rays are made
- all are emitted from unstable nuclei (in an attempt to make them more stable),known as radioactive decay.
- It is spontaneous and random, there is no (current) way of detecting when an unstable nucleus will decay and there is no way of speeding up/slowing down the process as it is completely unaffected by physical conditions (such as temperature or pH) or by and sort of chemical reactions/bondings.
what is background radiation
the radiation that exists around us all the time
background radiation from rock
Radon gas
background radiation from space
cosmic rays
background radiation from biological material
Carbon-14
background radiation from food and drink
radioactive material
what is meant by half life
half-life is the time taken for half of the radioactive atoms now present to decay.
uses of radioactivity in medical tracer
– Radioactive tracer put in body (swallowed/injected)
– Detector put around body
– Computer generates an image
uses of radioactivity in sterilisation
- Medical equipment irradiated
- Kills all living matter on tools (e.g. bacteria)
uses of radiation in radiotherapy
High doses of radiation are directed at cancer cells
Cancer cells are killed
whats the difference between contamination and irradiation
- Contamination:
Occurs when material that contains radioactive atoms is deposited on materials, skin, clothing, or any place where it is not desired. - Irradiation:
The process by which an object is exposed to radiation.
the dangers of ionising radiations
- radiation can cause mutations in living organisms
- that radiation can damage cells and tissue
why is the disposal of radioactive waste dangerous?
it emits radioactive particles, which if not properly managed can be a risk to human health and the environment.
what is done to make disposal of radioactive waste more safe?
Radioactive waste with a long half-life is buried underground to prevent it from being released into the environment
nuclear reactions, including fission, fusion and radioactive decay can be a source of
energy
nuclear fission
- A “slow” neutron is absorbed by a uranium-235 nucleus.
- making the nucleus unstable
- splits apart to form two smaller daughter nuclei, and a few neutrons
- If more than one neutron from each fission causes fission in surrounding nuclei, the reaction escalates.
- This is called chain reaction.
- This involves sudden release of enormous heat energy and radiation.
what is sheilding?
Reactor vessel is made of steel and surrounded by a concrete layer about 5 meters thick.
This prevents any radiation escaping, even neutrons.
what is the scource of energy for our sun and all stars
nuclear fusion
in the sun, ____ undergoes nuclear fusion to create ____
hydrogen, helium
why does the moon have a weaker gravidational feild strength
The Moon has less mass than the Earth, so its gravitational field is much weaker – approx 1/6th of the Earth’s.
why does the moon orbit the earth?
According to Newton, there is an attractive gravitational force between any two objects– pulling them together
Moons and artificial satellites are attracted to their planets, and so are pulled towards them.
This gravitational force keeps them moving in curved paths called orbits. The Moon does not crash into the Earth, and the planets do not crash into the Sun because they are moving.
differences between the orbit of the moon and the planets and the comets
Moons: They orbit planets, have an elliptical orbit.
Planets: They orbit stars, have an elliptical orbit.
Comets: They orbit stars, have a highly elliptical orbit.
hottest to coolest colours
blue - white - yellow - orange - red
evolution of stars of similar mass to the Sun stages:
- nebula
- star (main sequence)
- red giant
- white dwarf.
