Chapter 20: Electric Current, Resistance, and Ohm's Law

AC Current

current that fluctuates sinusoidally with time, expressed as I = I₀ sin 2πft, where I is the current at time t, I₀ is the peak current, and f is the frequency in hertz

AC voltage

voltage that fluctuates sinusoidally with time, expressed as V = V₀ sin 2πft, where V is the voltage at time t, V₀ is the peak voltage, and f is the frequency in hertz

Alternating Current

(AC) the flow of electric charge that periodically reverses direction

Ampere

(amp) the SI unit for current; 1 A = 1 C/s

Bioelectricity

electrical effects in and created by biological systems

Direct Current

(DC) the flow of electric charge in only one direction

Drift velocity

the average velocity at which free charges flow in response to an electric field

Electric Current

the rate at which charge flows, I = ΔQ/Δt

Electric Power

the rate at which electrical energy is supplied by a source or dissipated by a device; it is the product of current times voltage

Electrocardiogram (ECG)

usually abbreviated ECG, a record of voltages created by depolarization and repolarization, especially in the heart

microshock sensitive

a condition in which a person’s skin resistance is bypassed, possibly by a medical procedure, rendering the person vulnerable to electrical shock at currents about 1/1000 the normally required level

nerve conduction

the transport of electrical signals by nerve cells

ohm

the unit of resistance, given by 1Ω = 1 V/A

Ohm’s Law

an empirical relation stating that the current I is proportional to the potential difference V, ∝ V; it is often written as I = V/R, where R is the resistance

Ohmic

a type of a material for which Ohm's law is valid

Resistance

the electric property that impedes current; for ohmic materials, it is the ratio of voltage to current, R = V/I

Resistivity

an intrinsic property of a material, independent of its shape or size, directly proportional to the resistance, denoted by ρ

rms current

the root mean square of the current, 𝐼rms=𝐼0/√2 , where I₀ is the peak current, in an AC system

rms voltage

the root mean square of the voltage, 𝑉rms=𝑉0/√2 , where V₀ is the peak voltage, in an AC system

semipermeable

property of a membrane that allows only certain types of ions to cross it

shock hazard

when electric current passes through a person

short circuit

also known as a “short,” a low-resistance path between terminals of a voltage source

simple circuit

a circuit with a single voltage source and a single resistor

temperature coefficient of resistivity

an empirical quantity, denoted by α, which describes the change in resistance or resistivity of a material with temperature

thermal hazard

a hazard in which electric current causes undesired thermal effects

Ampere (A)

SI unit for current equal to one coulomb per second.

Relationship of Current to Drift Velocity

the proportionality between the electric current flowing through a conductor and the drift velocity of charge carriers, indicating how the movement of these carriers contributes to the current

a voltage or IR drop across a resistor,

resulting in a decrease in current flow through the circuit.

The resistance 𝑅 of a cylinder

is defined as the ratio of voltage to current flowing through it, reflecting how much it opposes the flow of electric current.

Temperature Affecting Resistivity

describes how the resistivity of a material typically increases with temperature, impacting its ability to conduct electricity.

The energy used by a device with a power 𝑃 over a time 𝑡

is known as electrical energy, calculated as the product of power and time, expressed in joules.

Average AC Power

is the measure of the effective power consumption in an alternating current (AC) circuit, calculated by averaging the instantaneous power over one complete cycle.

Ohm’s law for AC

relates AC voltage (V) and AC current (I) to impedance (Z) in alternating current circuits, given by V = IZ.

Expressions for the average power of an AC circuit

𝑃ave=𝐼rms⁢𝑉rms, 𝑃ave=𝑉2rms𝑅, and 𝑃ave=𝐼2rms⁢𝑅, analogous to the expressions for DC circuits.