Whole Course Flashcards
What is the acceleration due to gravity?
When on Earth, acceleration due to gravity is 9.8m/s/s downwards or -9.8m/s/s.
What is the gradient of a displacement-time graph?
Velocity.
What is the gradient of a velocity-time graph?
Acceleration.
Describe the forces acting on a sky diver
- Accelerate because there is a force due to gravity (weight) downwards.
- Air resistance increases with speed, reducing acceleration.
- Air resistance balances weight, falling at a terminal speed.
- Parachute increases air resistance, Fun upwards so slows down.
- Air resistance decreases with speed, reaches a new terminal speed.
What is the law of conservation of momentum?
In the absence of external forces, total momentum just before an event is the same as total momentum just after the event.
In an elastic collision…
…kinetic energy is conserved.
In an inelastic collision…
…kinetic energy decreases.
In an explosion…
…kinetic energy increases.
What is the area under a force-time graph?
- Impulse of the force
2. Change in momentum
What is the Doppler effect?
The change in frequency observed when a source of sound waves is moving relative to an observer.
What is the redshift of a galaxy?
The change in wavelength divided by the emitted wavelength. For slow moving galaxies, it is also the ratio of the recessional velocity of the galaxy to the velocity of light.
What does the Doppler Effect cause?
Shifts in wavelength of sound and light.
How is the light from objects moving away from us shifted?
It is shifted towards longer wavelengths (redshift).
What does Hubble’s law allow us to estimate?
Hubble’s law allows us to estimate the age of the universe.
What lead to the theory of the expanding universe?
Measurements of the velocities of galaxies and their distance from us.
How can the mass of a galaxy be estimated?
By the orbital speed of the stars within it (mass of galaxy is directly proportional to orbital speed of stars within it).
What evidence is there for the existence of dark matter?
Estimations of the mass of galaxies suggest there is more matter than astronomers can detect.
What evidence is there for the existence of dark energy?
The accelerating rate of expansion of the universe tells us there must be something overcoming the force of gravity.
Temperature of stellar objects.
Temperature of stellar objects is related to the distribution of emitted radiation over a wide rage of wavelengths.
Peak wavelengths of this distribution is shorter for hotter objects than for cooler objects.
Hotter objects emit more radiation per unit surface area per unit time than cooler objects.
What evidence is there for the Big Bang theory and the subsequent expansion of the universe?
Cosmic microwave background radiation (CMBR) is uniformly distributed across the universe; the abundance of the elements hydrogen and helium; the darkness of the sky (Olber’s paradox); and the large number of galaxies showing redshift rather than blueshift.
What is a.c.?
A current which changes direction and instantaneous value with time.
What is electric current?
Electric current is the rate of flow of charge.
What is potential difference (voltage)?
The energy required to move one coulomb of charge between two points in the electric field.
What is power?
Power is the rate of transformation of energy.
Open circuit
The circuit is incomplete so the current is zero.
Short circuit
The two terminals of a cell are connected with just a wire so the external resistance is zero.
What is the EMF of a source?
The electrical energy supplied to each coulomb of charge passing through the source.
What is resistance?
Resistance is the opposition to the flow of electrons.
A capacitor of 1 farad will…
…store 1 coulomb of charge when the p.d. across it is 1 volt.
What does the total energy stored on a capacitor equal?
The area under a charge-potential difference graph.
How does temperature affect the conductivity of a semiconductor?
Increasing the temperature increases the conductivity of a semiconductor.
Why are semiconductors doped?
Semiconductors may be doped with specific impurities to increase their conductivity, resulting in p-type and n-type semiconductors.
When is a p-n junction formed?
A p-n junction is formed when a semiconductor contains the two types of doping (p-type and n-type) in adjacent layers.
Biasing
Forward bias reduces the electric field in a p-n junction.
Reverse bias increases the electric field in a p-n junction.
What is the standard model?
It is a model of fundamental particles and interactions.
Where does evidence for the existence of quarks come from?
High-energy collisions between electrons and nucleons, carried out in particle accelerators.
Antimatter
In the standard model, every particle has an antiparticle.
The production of energy in the annihilation of particles is evidence for the existence of antimatter.
What are electric fields?
Electric fields are areas where charged particles experience a force.
Where do electric fields exist?
Electric fields exist around charged particles and between charged parallel plates.
What produces a magnetic field?
A moving charge produces a magnetic field.
Particle accelerators
Electric fields are used to accelerate the charged particles.
Magnetic fields are used to deflect the charged particles.
High-energy collisions of charged particles produce other particles.
Nuclear fusion
Nuclear fusion reactors require charged particles at a very high temperature (plasma) which have to be contained by magnetic fields.
What evidence is there for the particulate model of light?
The photoelectric effect is evidence for the particulate model of light.
Photoemission
Photons of sufficient energy can eject electrons from the surface of materials.
What is threshold frequency?
The minimum frequency of a photon required for photoemission.
What is the work function of a material?
The minimum energy of a photon required to cause photoemission.
What evidence is there for the wave model of light?
Interference is evidence for the wave model of light.
What are coherent waves?
Waves with a constant phase relationship.
What is the absolute refractive index of a medium?
The ratio of the speed of light in a vacuum to the speed of light in the medium.
Refractive index and frequency
As the frequency of incident radiation increases, the refractive index of a medium increases.
What is the critical angle?
The angle of incidence which produces an angle of refraction of 90 degrees.
When does total internal reflection occur?
Total internal reflection occurs when the angle of incidence is greater then the critical angle.
What is irradiance?
Irradiance is the power per unit area incident on a surface.
Irradiance and distance
The irradiance is inversely proportional to the square of the distance from a point source.
What evidence is there for the elements present in the Sun’s outer atmosphere?
The absorption lines (Fraunhofer lines) in the spectrum of sunlight provide evidence for the composition of the Sun’s outer atmosphere.
