3.1.2 - Sensing (A-Level Physics OCR B H557)

#3.1.2a(i)

current as the flow of charged particles

#3.1.2a(ii)

potential difference as energy per unit charge

#3.1.2a(iii)

resistance and conductance, including series and parallel combinations

#3.1.2a(iv)

the effect of internal resistance and the meaning of e.m.f.

#3.1.2a(ix)

conservation of charge and energy.

as represented by Kirchhoff’s first and second law

#3.1.2a(v)

dissipation of power in electric circuits

#3.1.2a(vi)

the relationship between potential difference and current in ohmic resistors (Ohm’s law)

#3.1.2a(vii)

the action of a potential

#3.1.2a(viii)

simple electrical behaviour of metals, semiconductors and insulators in terms of the number density of mobile charge carriers

#3.1.2b

Make appropriate use of:

(i) the terms: e.m.f, potential difference, current, charge, resistance, conductance, series, parallel, internal resistance, load, resistivity, conductivity, charge carrier number density

(ii) and recognise standard circuit symbols

by sketching and interpreting:

(iii) graphs of current against potential difference and graphs of resistance or conductance against temperature for ohmic and non-ohmic devices or components.

#3.1.2c(i)

$R = \dfrac{V}{I}$ , $G = \dfrac{I}{V}$ ,

$V = \dfrac{W}{Q} = \dfrac{P}{I}$ ,

$P = IV = I^2R$ ,

$W = VIt$ ,

$V = ε - Ir_{internal}$

Learners will also be expected to recall the equations for R and G. Epsilon is used as the symbol for e.m.f. to avoid confusion with E which is used for energy and electric field. The ASE guide ‘Signs symbols and systematics’ details E as the correct symbol for e.m.f. and this will be credited in all examinations.

#3.1.2c(ii)

$I = \dfrac{ΔQ}{Δt}$ ,

$\dfrac{1}{G} = \dfrac{1}{G_1} + \dfrac{1}{G_2} + ...$

$G = G_1 + G_2 + ...$

$R = R_1 + R_2 + ...$

$\dfrac{1}{R} = \dfrac{1}{R_1} + \dfrac{1}{R_2} + ...$

#3.1.2c(iii)

$R = \dfrac{ρL}{A}$ ; $G = \dfrac{σA}{L}$

#3.1.2c(iv)

simple cases of a potential divider in a circuit using:

$V_{out} = \dfrac{R_2}{R_1+R_2} × V_{in}$ and

$\dfrac{V_1}{V_2} = \dfrac{R_1}{R_2}$

Learners will be expected to recall the proportionality of potential difference and resistance in a series circuit

#3.1.2d(i)

investigating electrical characteristics for a range of ohmic and non-ohmic components using voltmeters and ammeters

links to 3.1.2a(vi), b(iii), PAG3

#3.1.2d(ii)

determining the resistivity or conductivity of a metal

links to 3.1.2c(iii), PAG3

#3.1.2d(iii)

use of potential divider circuits, which may include sensors such as thermistor, LDR

links to 3.1.2a(vii), PAG4

#3.1.2d(iv)

the calibration of a sensor or instrument

links to 3.1.2a(vii), c(iii), PAG3

#3.1.2d(v)

determining the internal resistance of a chemical cell or other source of e.m.f.

links to 3.1.2a(iv), PAG3

A-Level Physics OCR B H557

3.1.2: Sensing