Chapter 6: Circuits Flashcards
By historical convention, which direction is current flow?
Because of historical conventions, current is considered the flow of positive charge.
Even though only negative charges are actually moving.
Any conductive substance may act as a medium through which current can pass.
What is metallic conductivity what is electrolytic conductivity?
Conductivity can be divided into two categories: metallic and electrolytic conductivity.
Metallic conductivity is seen in solid metals and molten forms of some salts.
Electrolyte conductivity is seen in solutions.
What is conductance? What is the SI unit for conductance?
Conduction is the reciprocal of resistance. The SI unit for conductance is the siemens (S), sometimes siemens per meter (S/m).
Recall where metals are found on the periodic table. Relate this to ionization energy and thus metals tendency with electrons.
Remember that the metals are found on the left side of the periodic table. These are at the atoms with the lowest ionization energies; thus it is easiest for these atoms to lose electrons. Due to this weak hold (due to low ionization energies) electrons are free to move around in the metal, conducting electrical charges.
What is an electrical conductor? What material makes good electrical conductors?
An electrical conductor allow free flow of electric charge within them. Metals can easily lose one or more of their outer electrons, which are then free to move around in the larger collection of metal atoms, this being good electrical and thermal conductors.
How are metallic bonds visualized?
Metallic bonds are often visualized as a sea of electrons flowing over and past a rigid lattice of metal cations.
What does the strength of electrolytic conductivity rely on?
The strength of electrolytic conductivity relies on the concentration of solution.
For example, distilled deionized water has such a low ion concentration that it may be considered an insulator.
Because concentration and conductivity are directly related, this method is often used to determine ionic concentrations in solutions, such as blood.
What is current? How do we calculate the magnitude of current? What is the SI unit of current?
Current is the flow of charge between two points at different electrical potentials connected by a conductor.
The magnitude of current is the amount of charge passing through a conductor per unit time.
The unit of current is the ampere and one ampere equals one coulomb per second.
There are two patterns of current flow. What are they?
Direct current (DC) in which the charge flows in one direction only (household batteries)
Alternating current (AC) in which the flow changes direction periodically (long distance power, such as power to a home)
Charge is transmitted by a flow of electrons in a conductor. Regarding electrical potential, which direction will an electron move?
Because electrons are negatively charged, they move from a point of lower electrical potential to a point of higher electrical potential (and in doing so reduce their electrical potential energy).
What do we call voltage when no charge is moving between two terminals of a cell that are at different potential values?
When no charge is moving between the two terminals of a cell that are at different potential values, the voltage is called the electromotive force (emf).
Is electromotive force an actual force?
Electromotive force is not actually a force. It is a potential difference (voltage) and as such as units of volts (Joules/Coulomb), not Newtons.
Currents (and circuits in general) are governed by the laws of conservation. How so?
Charge an energy must be fully accounted for at all times and can be neither created nor destroyed.
What is Kirchhoff’s junction rule?
Kirchhoff’s junction rule states that at any point or junction in a circuit, the sum of currents directed into that point equals the sum of current directed away from that point. This is an expression of conservation of electrical charge and can be expressed as:
Example Kirchhoff’s junction rule page 214
What is Kirchhoff’s loop law?
Around any closed circuit loop, the sum of voltage sources will always be equal to the sum of voltage (potential) drops.
This is a consequence of the conservation of energy. All the electrical energy supplied by a source gets fully used up by the other elements within that loop. No energy appears, no energy appears that cannot be accounted for.
This law is in terms of voltage (joules/coulomb), not just energy (joules).
MCAT concept check 6.1 Current page 215 question 1
Also conductivity
Current is the movement of positive charge through a conductive material overtime and is given in Amperes (A = coulomb per second).
Voltage is a potential difference between two points and is given in volts (V = J/C).
Electromotive force refers to the potential difference of the voltage source for a current, usually a battery, and is given in volts (V = J/C)
Conductivity is the reciprocal of resistance and is a measure of permissiveness to current flow and it is measured in siemens (S, sometimes S/m)
MCAT concept check 6.1 Current page 215 question 2
The sodium chloride solution likely has a higher conductivity because it is a salt and will increase the ion content of water. Glucose does not dissociate, and therefore it has a near zero impact on conductivity (effectively no net charge in water).
MCAT concept check 6.1 Current page 215 question 3 and 4
True. This is a statement of Kirchhoff junction rule. Current in = Current out
False. While the voltage sources and voltage drops are equal in any closed loop, this is not necessarily true for the entire circuit. For example, a 9 V battery that powers 10 lightbulbs in parallel has a 9 V voltage source and a 9 V drop across each lightbulb, a total of 90 V of drop across all of the lightbulbs combined.
What is resistance?
Resistance is the opposition within any material to the movement and flow of charge. Electrical resistance can be thought of like friction, air resistance, or viscous drag: in all of these cases, motion is being opposed.
Materials that offer almost no resistance are called conductors, and those materials that offer very high resistance are called insulators.
What is a resistor?
Conductive materials that offer amounts of resistance between conductors and insulators are called resistors.
A resistor is an electrical component that limits or regulates the flow of electrical current in an electronic circuit.
The resistance of a resistor is dependent upon certain characteristics of the resistor. What are these characteristics (
Resistivity, length, cross-sectional area, and temperature are the characteristics of a resistor that characterize its resistance.
What is the equation for resistance?
What is resistivity?
The number that characterizes the intrinsic resistance to current flow in a material is called resistivity. The SI unit for resistivity is the ohm-meter.