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Electric Current - Objectives
- Errors and uncertainty
- Electric current
- Potential difference
- Ohm’s law
- Resistance and resistivity
Candidates should be able to:
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- understand the nature of random and systematic errors
- understand and use the terms precision, repeatability, reproducibility, resolution and accuracy
- understand that absolute, fractional and percentage errors represent uncertainty in the final answer for a quantity
- how to combine absolute and percentage uncertainties
- represent uncertainty in a data point on a graph using error bars
- determine the uncertainties in the gradient and intercept of a straight-line graph
- understand that individual points on a graph may or may not have associated error bars
- understand electric current as a net flow of charged particles
- understand the concept of charge in terms of the product of current and time; electric current as the rate of flow of charge
- recall and use ΔQ = IΔt
- appreciate the difference between the directions of conventional current and of electron flow.
- define potential difference and the volt in terms of energy transfer; potential difference as work done per unit charge
- recall and use and V=W/Q
- recall the current-voltage characteristics for an ohmic conductor, a semiconductor diode and a filament lamp; candidates should have experience of the use of a current sensor and a voltage sensor with a data logger to capture data from which to determine and explain V/I curves
- NB. Questions can be set where either I or V is on the horizontal axis of the characteristic graph
- define resistance and the ohm; resistance is defined by R =V/I
- state Ohm’s law; know Ohm’s law as a special case where I α V under constant physical conditions
- define resistivity.
- recall and use ρ = RA/l
- Description of the qualitative effect of temperature on the resistance of metal conductors and thermistors. Applications (e.g. temperature sensors and resistance-temperature graphs). (ntc thermistors only)
- Superconductivity as a property of certain materials that have zero resistivity at and below a critical temperature, which depends on the material.
- Applications (e.g.very strong electromagnets, the reduction of energy loss in transmission of electric power). Critical field will not be assessed.
- REQUIRED PRACTICAL - determination of the resistivity of a wire using a micrometer, ammeter and voltmeter