Ch 6 - Circuits Flashcards
What is a current?
the movement of charge that occurs between 2 points that have different electrical potentials ( A = C/s)
I = Q/t
What is the difference between the conventional definition of a current and reality?
- by convention, current is defined as the movement of positive charge from the high potential end of a voltage source to the low potential end
- in reality, it is negatively charged particles (electrons) that move in a circuit, from low potential to high potential
Where does currents flow?
only in conductive materials
What is the difference between metallic conduction, electrolytic conduction, and insulators?
- metallic relies on uniform movement of free electrons in metallic bonds
- electrolytic relies on the ion concentration of a solution
- insulators are materials that do not conduct a current
What is Kirchhoff’s law?
express conservation of charge and energy
What is Kirchhoff’s junction rule?
states that the sum of currents directed into a point within a circuit equals the sum of the currents directed away from that point
I into junction = I leaving junction
What is Kirchhoff’s loop rule?
states that in a closed loop, the sum voltage sources is always equal to the sum of voltage drops
- if all the voltage wasn’t used up in each loop of the circuit, then the voltage would build after each trip around the circuit, which is impossible
V source = V drop
- the total potential difference around any closed loop is 0
What is resistance?
opposition to movement of electrons through a material
R = (resistivity x length)/cross sectional area
R = pL/A
What are resistors?
conductive materials with a moderate amount of resistance that slow down electrons without stopping them
What is Ohm’s law?
states that for a given resistance, the magnitude of the current through a resistor is proportional to the voltage drop across the resistor
V = IR
What is the purpose of combining resistors in a circuit and how can they be combined?
- can be combined to calculate the equivalent resistance of a full or partial circuit
- resistors in series are additive and sum together to create the total resistance of a circuit
- resistors in parallel cause a decrease in equivalent resistance of a circuit
What does the amount of dissipated power across each resistor in a circuit depend on?
dependent on the current through the resistor and the voltage drop across the resistor
What are capacitors?
have the ability to store and discharge electrical potential energy
How is capacitance in parallel plate capacitors determined?
by the area of the plates and the distance between the plates
What do capacitors in series cause?
a decrease in the equivalent capacitance of a circuit
What do capacitors in parallel create?
they sum together to create a larger equivalent capacitance
What are dielectric materials?
insulators placed between the plates of a capacitor that increase capacitance by a factor equal to the material’s dielectric constant, k
C’ = kC
- can never decrease capacitance, k never less than 1
What are ammeters?
inserted in series in a circuit to measure current; they have negligible resistance
- minimum impact on circuit
What are voltmeters?
inserted in parallel in a circuit to measure a voltage drop; they have very large resistance
- minimum impact on circuit
What are ohmmeters?
inserted around a resistive element to measure resistance; they are self powered and have negligible resistance
What is voltage?
potential difference between 2 points (Volts = J/C)
What is electromotive force (emf)?
the potential difference of the voltage source for a circuit, usually a battery, and is given in volts
What is conductivity?
the reciprocal of resistance and is a measure of permissiveness to current flow, measured in siemens (S)
Which likely has a higher conductivity and why: 1 M glucose and 0.25 M NaCl?
NaCl higher 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
