CAP 3 Flashcards
Why is it important to test by experiment the prediction of a scientific theory?
if a reliable experiment supports a theory, the theory can be accepted, and extended on
if a reliable experiment does not support a theory, the theory must be changed
What is the strong nuclear force?
The fundamental force that keeps the nucleus stable by counteracting the electrostatic force of repulsion between protons
What is meant by the emf of a battery? (Explain in two ways)
emf is the chemical energy transferred into electrical energy in the battery per unit charge passing through
or the pd across terminals when no current is passing through the battery
Suggest how two lamps can have different power rating but have the same intensity output
in lamps energy is wasted as heat (thermal energy)
one lamp may waste more energy than the other, as in less energy is converted into light
State what is meant by the centre of mass.
the centre of mass is the point through which the line of action of a force has no turning effect
it is where the mass of the body can be considered to be concentrated
State what is meant by superconductivity.
Explain the required conditions for the material to become superconducting
superconductivity means a material has zero resistivity, and zero resistance at or below a critical temperature
resistivity decreases with temperature
so the material becomes superconducting when you reach the critical temperature
State the role of exchange particles in the creation of forces between particles
The force arises when the exchange particle moves between the other particles
State the names of the particles that are produced when a muon decays.
Electron + an electron antineutrino + muon neutrino
State on application of a polarising filter and give a reason for its use
Polaroid sunglasses - to reduce glare
Name a way to detect if an electron has been released from an experiment
Using a cloud chamber
Give two properties of hadrons that distinguish them from leptons.
hadrons experience the strong interaction, leptons don’t
hadrons are made up of quark, so are not fundamental, leptons are fundamental
For a sound wave, explain what is meant by wavelength
wavelength is shortest distance between two points in phase
it is the distance between two adjacent compressions (or rarefactions)
Explain, in terms of electron motion, why the I–V characteristic for the filament lamp is a curve.
An increase in current/voltage leads to an increase in temperature, as electrical energy is converted into heat energy
So the metal ions vibrate with increased amplitude
And therefore an increase in the rate of collisions of the lattice ions with electrons
This impedes the movement of electrons through the lamp
So the resistance increases as shown by V being not proportional to I on the graph
Explain why the unloading line on a force/extension graph of a material that has been plastically deformed is parallel to the loading line, but doesn’t run through the origin
Plastic deformation has produced permanent extension
There has been re-alignment of bonds in materials hence the intercept is non-zero
But the gradient is the same because after extension the force between bonds is identical to before (ie the stiffness constant hasn’t changed)
Explain why it is necessary for many teams of scientists and engineers to collaborate in order for advances to be made in particle physics.
results of experiments must be independently peer reviewed before they are accepted ✔
particle accelerators are very expensive and collaboration helps to spread the cost of building them ✔
many skills and disciplines are required (which one team are unlikely to have) ✔
lots of data to process (so more teams needed) ✔
Explain what is meant by the internal resistance of the battery.
the resistance of the materials within the battery
It is the hindrance to flow of charge in battery
Explain what is meant by a progressive wave
A wave transfers energy from one point to another ✔
without transferring material ✔
Explain how the resistance of a lamp varies as the voltage across it is increased from zero to its working voltage
As voltage increases, temperature increases. The lattice ions are vibrating with increased amplitude, so there is an increased frequency of collisions of eletrons with the lattice ions, therefore resistance increases.
Explain how a bright line is formed by the diffraction grating at the first-order diffraction angle
light from each slit superpose
light from adjacent slits have a path difference of one wavelength
at this angle all the waves are in phase
constructive interference occurs
During the photoelectric effect, explain why, when ultraviolet light is shone on a positively charged plate, no charge is lost by the plate.
The process involves the ejection of electrons which are negatively charged
Any electrons ejected will only make the positive charge greater
Describe what is likely to happen to a positron shortly after its creation.
It will meet an electron, and annihilate. It’s mass will be converted into two or more photons travelling in opposite directions in order to conserve momentum
What is potential difference?
Potential difference is the work done moving a unit charge between 2 points in a circuit
What is resistance?
Resistance is how difficult it is for current to flow through an appliance
R = V / I
What is Ohm’s law?
Current is directly proportional to potential difference providing physical conditions remain constant
What is a diode?
A diode is an appliance that only allows current to flow in one direction
What is the minimum voltage required across a diode in order for it to pass a significant current?
Approximately 0.7V
Why should voltmeters have infinite resistance?
So that no current flows through it and all the current flows through the appliance
Why should ammeters have zero resistance?
So that there would be 0 potential difference across the ammeter and no energy is lost across it
So it does not affect the circuit
What is an LDR?
A light dependent resistor
It is a semiconductor that is sensitive to light
As light intensity increases, its resistance decreases
What is resistivity?
The resistance of a 1m cylinder with a cross sectional area of 1m^2
What is the purpose of a potential divider
To provide variable potential difference
Or to provide a constant specific potential difference
What is lift?
An upward force which acts on objects travelling in a fluid, it is caused by the object creating a change in direction of fluid flow and acts perpendicular to the direction of fluid flow
What is tensile strain?
Extension produced per unit length
What is tensile stress?
Force applied per unit cross sectional area
What is breaking stress?
The minimum stress needed to break a material
What is meant when a material is described as brittle?
It doesn’t deform plastically but breaks when the stress reaches a certain value
What is the elastic limit?
The maximum amount that a material can be stretched by a force and still return to its original length when the force is removed
Or the force above which a material will be plastically deformed
What does the area underneath. a force extension graph represent?
The work done to deform the material
How is the dissipation of energy in plastic deformation used to design safer vehicles?
Crumple zones deform plastically in a crash using the car’s kinetic energy so less is transferred to the passengers
Seat belts stretch to convert the passenger’s kinetic energy into elastic strain energy
What is a ductile material?
A material that can undergo a large amount of plastic deformation before fracturing
What is a a stationary wave
A stationary wave is a wave which does not transfer any energy
Its positions of maximum and minimum AMPLITUDE are constant (called anti-nodes and nodes respectively)
How are stationary waves produced?
A stationary wave is formed from the SUPERPOSITION of 2 progressive waves, travelling in opposite direction IN THE SAME PLANE, with the same frequency and wavelength, and similar amplitude.
Where the phase difference between the two waves is an even multiple of half wavelengths, the two waves are in phase. They constructively interfere, superposition of the two waves results in a point of maximum amplitude called an antinode
Where the phase difference between the two waves is an odd multiple of half wavelengths, the two waves are anti phase. They destructively interfere, superposition of the two waves results in a point of minimum amplitude called a node
Describe briefly what Young’s double-slit experiment was?
A SINGLE light source is directed towards to slits, which each act as a COHERENT light source. The light interests constructively and destructively to create an interference pattern.
Why does an interference pattern form when light is passed through as slit?
The light diffracts as it passes through the slit
Waves from the edge of the slit travel difference distances to the screen than the in the middle of the slit
So there is a path difference between them
A path difference means a phase difference
(phase difference/superposition/constructive/destructive/light/dark/interference)
Describe the single slit pattern
The central fringe has twice the width of those to either side
The central fringe has a MUCH larger intensity than those to either side
Explain the effect of increases the slit width on the central maximum in single slit diffraction?
The slit is not close to the wavelength in size, so less diffraction occurs
The central maximum becomes narrower and more intense
What is the purpose of the cladding in an optical fibre?
Protects core from scratches which would allow light to escape and degrade the signal
Allows total internal reflection as it has a lower refractive index than the core
How does signal degradation by absorption in an optical fibre affect the received signal?
Part of the signal’s energy is absorbed by the fibre so its amplitude is reduced
What is pulse broadening?
When the received signal is wider than the original
This can cause overlap of signals leading to information loss
How can modal dispersion be reduced?
Use a monomode fibre, so the possible difference is path lengths is smaller
How can both absorption and dispersion be reduced in an optical fibre?
Use an optical fibre repeater to regenerate the signal now and then
State the advantages of optical fibres over traditional copper wires
Signals can carry more information as light has a high frequency
No energy lost as heat
No electrical interference
Very fast
How did Young’s double slit experiment provide evidence for the wave nature of light?
Diffraction and interference are wave properties, hence the interference pattern of light shows light has wave properties
What is phase?
Phase is the position of a certain point on a wave cycle
