@?recall-questions

Recall Questions What is a photon?? A quantum of energy of electromagnetic radiation. What is the photoelectric effect?? The emission of electrons from a metal surface when illuminated with light. What is a photoelectron? An electron that has been removed from a metal by absorbing a photon. What is the work function?? The minimum energy required to release an electron from the surface of a metal. What is the threshold frequency?? The minimum frequency of light required to produce photoelectrons from a metal.

Recall Questions State what is meant by the superposition principle?? When two or more waves meet at a point, the resultant displacement is the vector sum of the displacements of the individual waves. State what is meant by coherent waves?? Waves that have a constant phase difference. State the conditions for two waves to be coherent?? The waves must be of the same type and have the same frequency. State what is meant by interference?? The superposition of waves from coherent sources.

Recall Questions State what is meant by a progressive wave?? A wave that transfers energy from one point in space to another without transferring matter. Compare transverse and longitudinal waves?? In tranverse waves, the oscillations are perpendicular to the direction of energy transfer. In longitudinal waves, the oscillations are parallel to the direction of energy transfer. They consist of compressions and rarefactions. Define the displacement of a wave?? Distance from the equilibrium position in a particular direction.

Recall Questions State Kirchoff’s second law and appreciate that this a consequence of conservation of energy?? Sum of the EMF is equal to the sum of the voltages. What can we say about the current through a component in series. Same for each compoent. What can we say about the p.d. across parallel branches in a circuit?? It is the same for each branch. How do you find the total EMF from cells connected in series with the same polarity?

Recall Questions Define potential difference?? Energy transfer per unit charge from electrical to other forms. Define the volt?? $$1V = 1JC^{-1}$$ Define electromotive force of a source such as a cell or a power supply?? Energy transfer per unit charge from chemical/other to electrical form. Define resistance?? $$\frac{\text{potential difference}}{\text{current}}$$ Define the ohm?? A component has a resistance of $1\Omega$ is a potential difference of $1V$ makes a current of $1A$ flow through it. Define resistivity of a material?

Recall Questions Define current?? Rate of flow of charge. Define the coulomb?? The SI unit of electrical charge. One Coulomb is defined as the amount of charge that passes in 1 second when the current is 1 ampere. What do we mean when we say charge is quantised?? It can only take certain values (always $ne$). If $n$ electrons are removed from a neutral object, what is its charge?? $$ne$$ What is an electrolyte?? A liquid containing charged ions.

Recall Questions State Newton’s first law?? The velocity of an object will only change if a resultant force acts on it. State the ways in which an object’s velocity might change?? An objet may accelerate, decelerate, or change direction. State Newton’s third law (long)?? When two objects interact, they exert forces on each other that are equal in magnitude, opposite in direction and of the same type. State the four features of a Newton’s third law pair of forces?

Recall Questions Define Hooke’s law?? The extension of a spring is directly proportional to the force applied, provided the elastic limit of the spring is not exceeded. Define extension?? The difference between the final and initial length of an object. Define elastic deformation?? The material returns to its original shape and size after any applied forces are removed. Define plastic deformation?? The material will not return to its original shape and size after any applied forces are removed.

Recall Questions Define work done (enerhgy transferred by a force)?? Work done = Force x distance moved in direction of force How much work is done on an object by a force acting at right angles to the direction of motion of an object?? None. Define power?? Rate of work done/Rate of energy transfer Define the Watt?? $$1W = 1Js^{-1}$$ Define the Joule?? Work done to move a force of $1N$ (through) a distance of $1m$ through the point of application.

Recall Questions Define 1N?? The force required to give a mass of $1kg$ an acceleration of $1ms^{-2}$. What is a resultant (net) force?? The vector sum of all the forces acting on an object. What is the relationship between resultant force and acceleration, assuming mass remains constant?? $$F = ma$$ Describe the motion of an object with a resultant force of $0N$ acting on it?? Zero acceleration (therefore stationary or constant velocity). What direction does friction/drag act in?

Recall Questions Define displacement?? Distrance travelled in a particular direction. Define velocity?? Rate of change of displacement. Define acceleration?? Rate of change of velocity. State the units of acceleration?? $$ ms^{-2} $$ Define instantaneous speed?? Displacement $\Delta s$, divided by time for a very short time interval, $\Delta t$. Define average speed?? Total displacement divided by the total time for journey. What does the gradient of a displacement-time graph represent?? Instantaneous velocity. What does the gradient of a velocity-time graph represent?