Capacitance

Nature of science:

Relationships: Examples of exponential growth and decay pervade the whole of science. It is a clear example of the way that scientists use mathematics to model reality. This topic can be used to create links between physics topics but also to uses in chemistry, biology, medicine and economics. (3.1)

• Capacitance
• Dielectric materials
• Capacitors in series and parallel
• Resistor-capacitor (RC) series circuits
• Time constant

Applications and skills:

• Describing the effect of different dielectric materials on capacitance
• Solving problems involving parallel-plate capacitors
• Investigating combinations of capacitors in series or parallel circuits
• Determining the energy stored in a charged capacitor
• Describing the nature of the exponential discharge of a capacitor
• Solving problems involving the discharge of a capacitor through a fixed resistor
• Solving problems involving the time constant of an RC circuit for charge, voltage and current

• Lightning is a phenomenon that has fascinated physicists from Pliny through Newton to Franklin. The charged clouds form one plate of a capacitor with other clouds or Earth forming the second plate. The frequency of lightning strikes varies globally, being particularly prevalent in equatorial regions. The impact of lightning strikes is significant, with many humans and animals being killed annually and huge financial costs to industry from damage to buildings, communication and power transmission systems, etc

Utilization:

• The charge and discharge of capacitors obeys rules that have parallels in other branches of physics including radioactivity (see Physics sub-topic 7.1)

Aims:

• Aim 3: the treatment of exponential growth and decay by graphical and algebraic methods offers both the visual and rigorous approach so often characteristic of science and technology
• Aim 6: experiments could include (but are not limited to): investigating basic RC circuits; using a capacitor in a bridge circuit; examining other types of capacitors; verifying time constant

• Only single parallel-plate capacitors providing a uniform electric field, in series with a load, need to be considered (edge effect will be neglected)
• Problems involving the discharge of capacitors through fixed resistors need to be treated both graphically and algebraically
• Problems involving the charging of a capacitor will only be treated graphically
• Derivation of the charge, voltage and current equations as a function of time is not required

Data booklet reference: