A Level Electronics Eduqas

Electrical quantities and units

Basics of Electrical Quantities

• Understand charge (Q) as a physical property of matter that causes it to experience a force when near other electrically charged matter, measured in coulombs (C).

• Know current (I) as the rate of flow of charge, measured in amperes (A).

• Recognise the potential difference (V) as the work done per unit charge, measured in volts (V).

• Understand the resistance (R) which opposes the flow of current, measured in ohms (Ω).

• Identify power (P) as the rate of energy transfer, or work done, measured in watts (W).

Basic and Derived Electrical Quantities

• Define capacitance (C) as the ability of a body or device to store an electrical charge, measured in farads (F).

• Know inductance (L) as the property in an electric circuit where a change in the current induces an electromotive force, measured in henries (H).

• Recall frequency (f) as the number of cycles of a periodic wave occurring per unit time, measured in hertz (Hz).

Mathematical Relationship Between Electrical Quantities

• Application of Ohm’s law, V = I x R which states the voltage across a resistor is directly proportional to the current flowing through it.

• The relation between power, voltage and current P = V x I.

• Know the application of Kirchhoff’s laws, these enable the currents and voltages in any network of resistors to be calculated.

Units and Conversions

• Familiarise with the metric prefixes (pico, nano, micro, milli, kilo, mega, giga, tera) used for the electrical and electronic units, their symbols and values.

• Understand changing standard units to other units. Like, changing seconds (s) to milliseconds (ms), microseconds (µs) or nanoseconds (ns) and vice versa.

• Converting frequencies from hertz (Hz) to kilohertz (kHz), megahertz (MHz), or gigahertz (GHz), and vice versa.

• Know how to convert power units from watts (W) to milliwatts (mW), microwatts (µW), or nanowatts (nW), and vice versa.