Electric current is the flow of charge carriers (usually electrons) in a circuit.
Charge carriers have quantized charges, meaning they carry charges in discrete units.
The equation Q = It relates charge (Q) to current (I) and time (t).
For a current-carrying conductor, the equation I = Anvq can be used, where A is the cross-sectional area, n is the number density of charge carriers, v is the drift velocity, and q is the charge of each carrier.
9.2 Potential difference and power:
Potential difference (voltage) across a component is the energy transferred per unit charge.
The equation V = W/Q relates potential difference (V) to work done (W) and charge (Q).
Power (P) is the rate at which energy is transferred or transformed.
Power can be calculated using the equations P = VI, P = I2R, and P = V2/R.
9.3 Resistance and resistivity:
Resistance "R" is a measure of how a component or material opposes the flow of electric current.
Ohm's law states that the current flowing through a conductor is directly proportional to the potential difference across it, provided the temperature and other factors remain constant.
The equation V = IR relates potential difference (V), current (I), and resistance "R".
The I-V characteristics of different components can be observed, such as a metallic conductor (constant temperature), a semiconductor diode, and a filament lamp.
The resistance of a filament lamp increases as current increases due to the increase in temperature.
The resistance of a component can be determined by the equation R = ρL/A, where ρ is the resistivity, L is the length of the component, and A is the cross-sectional area.
The resistance of a light-dependent resistor (LDR) decreases as light intensity increases.
The resistance of a thermistor decreases as temperature increases (assuming a negative temperature coefficient).