Chapter 3 - Sensing Flashcards
What is an ion?
An atom or molecule with a net electric charge due to the loss or gain of one or more electrons
What gives metals their electrical properties?
Te presence of metal ions and the movement of negative electrons
Define current.
The rate at which charge flows through a point in an electrical current, measure in amperes (A).
What is the equation for current?
Current (A) = change in charge (C) / change in time (s)
What is a Coulomb?
The S.I. unit of electrical charge. 1 C is the change flowing through a point in 1s where there is a current of 1 A.
What is Kirchhoff’s first law?
At any electrical junction, the total current into the junction = the total current out of the junction. I 1 + I 2 +I 3 …= I total
What is potential difference?
The potential energy difference per unit charge moving between two points.
What is the equation for potential difference in terms of work done and charge?
V = W / Q
What is dissipation?
A thermal energy transfer resulting in an increase in internal energy, often of the surroundings.
Explain Joule heating.
When a p.d. between ends of a wire accelerates free electrons, they move through the wire but don’t gain kinetic energy as they get obstructed by interactions with the positive ion cores of metal atoms. The potential energy lost does work on the wire, heating it.
What is the equation for work done in terms of voltage, current and time?
W = VIt
What is the equation for power?
P = W / t = IV = I^2 * R
What is power?
The rate at which energy is transferred, measured in Joules per second, which is the watt (W).
What is resistance?
A measure of the opposition to current flow in an electrical circuit, measured in Ohms.
What is the equation for resistance?
R = V / I
What is Ohm’s Law?
A law stating that electric current is proportional to voltage and inversely proportional to resistance.
What is conductance?
The degree to which an object conducts electricity, calculated as the ratio of the current which flows to the potential difference present. This is the reciprocal of the resistance, and is measured in Siemens (S).
What is the equation for conductance?
G = I / V or 1 / R
Equation for total resistance in series?
R = R1 + R2 + …
Equation for total resistance in parallel?
1 / R = 1 / R1 + 1 / R2 + …
Equation for total conductance in series?
1/G = 1/G1 + 1/G2 + …
Equation for total conductance in parallel?
G = G1 + G2 + …
Give three features of series circuit combination of components.
- > Same current
- > Shared p.d.
- > Resistances add
Give three features of parallel circuit combination of components.
- > Shared current
- > Same p.d.
- > Conductances add
What happens to the resistance of a component as it heats up?
Increases
