Motion, Energy & Charge

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PH1.1 BASIC PHYSICS

Content

• Units and dimensions
• Scalar and vector quantities
• Force
• Free body diagrams
• Movements and stability
• Equilibrium

AMPLIFICATION OF CONTENT Candidates should be able to:

1.1 (a) recall and use SI units,

1.1 (b) check equations for homogeneity using units,

1.1 (c) contrast scalar and vector quantities and give examples of each – displacement, velocity, acceleration, force, speed, time, density, pressure etc.,

1.1 (d) appreciate the concept of force and understand Newton's 3rd law of motion,

1.1 (e) use free body diagrams to represent forces on a particle or body,

1.1 (f) recall and use the relationship ΣF = ma in situations where mass is constant,

1.1 (g) add and subtract coplanar vectors, and perform mathematical calculations limited to two perpendicular vectors,

1.1 (h) resolve a vector into two perpendicular components,

1.1 (i) understand the concept of density, use the equation ρ=m/V to calculate mass, density and volume;

1.1 (j) understand and define the turning effect of a force;

1.1 (k) recall and use the principle of moments;

1.1 (l) understand and use centre of gravity, for example in simple problems including toppling and stability. Identify its position in a cylinder, sphere and cuboid (beam) of uniform density;

1.1 (m) understand that a body is in equilibrium when the resultant force is zero and the net moment is zero, and be able to perform simple calculations.

PH1.2 KINEMATICS

Content

• Rectilinear motion.

AMPLIFICATION OF CONTENT Candidates should be able to:

1.2 (a) define displacement, mean and instantaneous values of speed, velocity and acceleration,

1.2 (b) use graphical methods to represent displacement, speed, velocity and acceleration,

1.2 (c) understand and use the properties of displacement-time graphs, velocity-time graphs, acceleration-time graphs, and interpret speed and displacement-time graphs for non-uniform acceleration,

1.2 (d) derive and use equations which represent uniformly accelerated motion in a straight line,

1.2 (e) describe the motion of bodies falling in a gravitational field with and without air resistance − terminal velocity,

1.2 (f) recognise and understand the independence of vertical and horizontal motion of a body moving freely under gravity,

1.2 (g) describe and explain motion due to a uniform velocity in one direction and uniform acceleration in a perpendicular direction, and perform simple calculations.

PH1.3 ENERGY CONCEPTS

Content

• Work, Power and Energy.

AMPLIFICATION OF CONTENT Candidates should be able to:

1.3 (a) recall the definition of work as the product of a force and distance moved in the direction of the force when the force is constant; calculation of work done, for constant forces, when force is not along the line of motion ($WD=Fx \cos \theta$)

1.3 (b) understand that the work done by a varying force is the area under the Force-distance graph,

1.3 (c) recall and use Hooke's law $F = kx$, and apply this to (b) above to show that elastic potential energy is ${1 \over 2}Fx$ or ${1 \over 2} k{x^2}$,

1.3 (d) understand and apply the work–energy relationship $Fs={1 \over 2}m{v^2}-{1 \over 2}m{u^2}$ and recall that $E_k = {1 \over 2}m{v^2}$,

1.3 (e) recall and apply the principle of conservation of energy including use of gravitational potential energy mgΔh , elastic potential energy 1/2kx2, and kinetic energy 1/2 mv2,

1.3 (f) define power as the rate of energy transfer,

1.3 (g) appreciate that dissipative forces e.g. friction, viscosity, cause energy to be transferred from a system and reduce the overall efficiency of the system,

1.3 (h) recall and use Efficiency = Useful energy obtained/Energy input × 100%,

PH1.4 CONDUCTION OF ELECTRICITY

Content

• Electric charge.
• Electric current.
• Nature of charge carriers in conductors.

AMPLIFICATION OF CONTENT Candidates should be able to:

1.4 (a) understand how attraction and repulsion between rubbed insulators can be explained in terms of charges on the surfaces of these insulators, and that just two sorts of charge are involved;

1.4 (b) understand that the name positive charge was arbitrarily given to the sort of charge on an amber rod rubbed with fur, and negative to that on a glass rod rubbed with silk;

1.4 (c) recall that electrons can be shown to have a negative charge, and protons, a positive;

1.4 (d) explain frictional charging in terms of electrons removed from, or added to, surface atoms;

1.4 (e) recall that the unit of charge is the coulomb (C), and that an electron's charge, e, is a very small fraction of a coulomb;

1.4 (f) recall that charge can flow through certain materials, called conductors;

1.4 (g) understand that electric current is rate of flow of charge;

1.4 (h) recall and use the equation I = ΔQ/Δt;

1.4 (i) recall that current is measured in ampère (A), where A = Cs-1;

1.4 (j) understand and describe the mechanism of conduction in metals as the drift of free electrons;

1.4 (k) derive and use the equation I = nAve for free electrons.

PH1.5 RESISTANCE

CONTENT

• Relationship between current and potential difference.
• Resistance
• Resistivity.
• Variation of resistance with temperature for metals.
• Superconductivity
• Heating effect of an electric current.

AMPLIFICATION OF CONTENT Candidates should be able to:

1.5 (a) define potential difference and recall that its unit is the volt (V) where V = JC-1.

1.5 (b) sketch I – V graphs for a semiconductor diode, the filament of a lamp, and a metal wire at constant temperature;

1.5 (c) state Ohm's Law;

1.5 (d) define resistance;

1.5 (e) recall that the unit of resistance is the ohm (Ω), where Ω = VA-1;

1.5 (f) understand that collisions between free electrons and ions give rise to electrical resistance, and to a steady drift velocity under a given p.d.,

1.5 (g) recall and use ρ = RA/l and understand that this is the defining equation for resistivity;

1.5 (h) describe how to determine the resistivity of a metal experimentally;

1.5 (i) describe how to investigate experimentally the variation of resistance with temperature of a metal wire;

1.5 (j) recall that the resistance of metals varies almost linearly with temperature over a wide range;

1.5 (k) understand what is meant by superconductivity, and superconducting transition temperature;

1.5 (l) recall that not all metals show superconductivity, and that, for those that do, the transition temperatures are a few degrees above absolute zero (–273°C);

1.5 (m) recall that certain special materials (high temperature superconductors) have transition temperatures above the boiling point of nitrogen (–196°C), and can therefore be kept below their critical temperatures using liquid nitrogen;

1.5 (n) recall that superconducting magnets are used in particle accelerators, tokamaks and magnetic resonance imaging machines, and are expected soon to be used in some large motors and generators;

1.5 (o) understand that ordinarily (that is, above the transition temperature), collisions between free electrons and ions in metals increase the random vibration energy of the ions, so the temperature of the metal increases;

1.5 (p) recall and use P = IV = I^2R = V^2/R.

PH1.6 D.C. CIRCUITS

CONTENT

• Series and parallel circuits.
• Combination of resistors.
• The internal resistance of sources.
• The potential divider.

AMPLIFICATION OF CONTENT Candidates should be able to:

1.6 (a) understand and recall that the current from a source is equal to the sum of the currents in the separate branches of a parallel circuit, and that this is a consequence of conservation of charge;

1.6 (b) understand and recall that the p.d.s across components in a series circuit is equal to the p.d. across the supply, and that this is a consequence of conservation of energy;

1.6 (c) understand and recall that the p.d.s across components in parallel are equal;

1.6 (d) recall and use formulae for the combined resistance of resistors in series and parallel;

1.6 (e) derive and use the potential divider formula V/Vout or Vout/Vin = R/Rtotal;

1.6 (f) define the e.m.f. of a source and appreciate that its unit, the volt (V), is the same as that of potential difference.

1.6 (g) appreciate that sources have internal resistance and use the formula V = E − Ir

1.6 (h) calculate current and p.d.s in a simple circuit containing one cell or cells in series.