A-Level Physics Specification

OCR B H557

Section 3.1.2: Sensing

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#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(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

#3.1.2a(ix)

conservation of charge and energy.

as represented by Kirchhoff’s first and second law

#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=VIR = \dfrac{V}{I} , G=IVG = \dfrac{I}{V} ,

V=WQ=PIV = \dfrac{W}{Q} = \dfrac{P}{I} ,

P=IV=I2RP = IV = I^2R ,

W=VItW = VIt ,

V=εIrinternalV = 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=ΔQΔtI = \dfrac{ΔQ}{Δt} ,

1G=1G1+1G2+...\dfrac{1}{G} = \dfrac{1}{G_1} + \dfrac{1}{G_2} + ...

G=G1+G2+...G = G_1 + G_2 + ...

R=R1+R2+...R = R_1 + R_2 + ...

1R=1R1+1R2+...\dfrac{1}{R} = \dfrac{1}{R_1} + \dfrac{1}{R_2} + ...

#3.1.2c(iii)

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

#3.1.2c(iv)

simple cases of a potential divider in a circuit using:

Vout=R2R1+R2×VinV_{out} = \dfrac{R_2}{R_1+R_2} × V_{in} and

V1V2=R1R2\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