Electric Circuits

Question 1

Electric Circuits

Answer 1

Electric circuit: a closed path through which current passes; this requires at least a conductor (wire), voltage source (e.g., battery), and output device (e.g., bulb, resistor)

Question 2

Resistance and Resistors

Answer 2

Resistance (R): the measure of a material’s opposition to the movement of charge through the material; or how much the material resists current flow. The SI unit of resistance is an Ohm
Resistance of a homogeneous material increases with the length of the object and decreases with the diameter

Resistor: an object used in electric circuits that oppose the flow of current

Question 3

Ohm’s Law

Answer 3

Ohm’s Law: describes the relationship between current, voltage, and resistance in electric circuits
The voltage drop (i.e., potential difference across a resistor (V) is equal to the current (I) multiplied by the resistance (R):
V=IR

Since resistors oppose the flow of current, the electric potential after a resistor is lower than prior to the resistor, and is called a voltage drop. Work is done in current flowing across a resistor.

Question 4

Capacitance, Capacitors, and Dielectrics

Answer 4

Capacitor: an electrical device composed of two oppositely charged plate separated by a short distance that stores electrical energy by the separation of charge.

Capacitance: the ability of a capacitor to hold a charge

Dielectric: an insulating material that increases capacitance when placed between two plates of a capacitor by a factor called the dielectric constant (specific to the insulating material)

Question 5

Series Circuits

Answer 5

Series circuits: groups of resistors or capacitors connected in line along a single path; the current is equal throughout

Resistors in series are simply added to obtain total resistance:
Rtotal = R1 + R2 + R3

Capacitors are added inversely for total capacitance:
1/Ctotal = 1/C1 + 1/C2 + 1/C3

Question 6

Parallel Circuits

Answer 6

Parallel circuits: connected so that multiple paths exist for the flow of current; the voltage is equal in all parts

Resistors in parallel are added inversely to obtain total resistance:
1/Rtotal = 1/R1 + 1/R2 +1/R3

Capacitors in parallel are simply added for total capacitance
Ctotal = C1 + C2 + C3

Question 7

Kirchoff’s Laws

Answer 7

1. The sum of voltage drop across a circuit is equal to the sum of the voltage drop across each element of a circuit
2. The current entering any node (joining of wires) in a circuit is equal to the total current leaving that point