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Electric Current - Objectives

Content

• Errors and uncertainty
• Electric current
• Potential difference
• Ohm’s law
• Resistance and resistivity

Learning Outcomes

Candidates should be able to:

• 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