Circuits

Question 1

Ohm’s Law

Answer 1

• The current (I in Ampere or A) is proportional to voltage (U in Volt or V)

Question 2

Voltage (U)

Answer 2

• Voltage is a specific measure of potential energy that is always relative between two nodes.
• Measure in Volts
• A difference in potential.

Question 3

Voltage Source

Answer 3

• Provides a fixed voltage between two nodes.
• Ideal voltage source has an infinite supply of power, provides as much current as necessary to maintain the voltage.
• Ideal voltage sources imply a capability of providing infinite power while they also have zero internal resistance.

Question 4

Resistance (Ω)

Answer 4

-Measure of the opposition to current flow in an electrical circuit.
- Due to friction and collisions between the free electrons and other atoms in the wire.
- Where R = U/I (voltage/current).

Question 5

Resistivity (rho-ρ)

Answer 5

R = ρl/A
where R is R is resistance, ρ is resistivity, l is length, A is area. Unit is ohm meters.
- Resistance depends on several parameters, such as the size (length and cross-sectional area) of the wire, its material and its temperature.

Question 6

Kirchhoff’s Voltage Law

Answer 6

• The sum of voltages in a closed circuit is always 0.
• Ensure the correct polarity (positive or negative) for each reading of voltage between points.

Question 7

Resistors in Series

Answer 7

R(Series) = R(1) + R(2)…

Question 8

Current Law in Series

Answer 8

i(series)= i(1) = i(2)…

Question 9

Voltage in Series

Answer 9

u(series)= u(1) + u(2)…

Question 10

Voltage Divider

Answer 10

• A voltage source connected in series with two resistors of different values
• Measure the voltage over only one resistor
• U(in) =U1 + U2
• U(out)/U(in) = R1/ (R1 + R2)
• Only valid if no current or power is drawn out, assumes only measures the voltage

Question 11

Kirchhoff’s Current Law

Answer 11

• The algebraic sum of the currents entering and leaving a node (junction) of a network is zero.
• ∑ i(n) = 0
• Positive are considered the currents that enter the junction, while negative are the currents that leave.
• Applies to any part of the circuit.

Question 12

Branch

Answer 12

A series connection of elements that has the same current throughout its length.

Question 13

Node/Junction

Answer 13

A point in a circuit where three or more branches meet.

Question 14

Loop

Answer 14

Any closed path in a circuit. A large loop may contain parts of smaller loops.

Question 15

Charge (q)

Answer 15

• Electric charge is the physical property of matter that causes it to experience a mechanical force when placed inside an electric field.
• Charges of the same type repel.
• The net charge of a body is the algebraic sum of positive and negative charges.
• Unit is Coulombs

Question 16

Current (I)

Answer 16

• Continuous movement of electric charge through the conductors of a closed circuit.
• Current is defined as the time-rate of flow of charge through a cross section of a conductor. I = dq/dt
• Current is “flow”, measured in Ampere (A).

Question 17

Current Source

Answer 17

• A current source is a source that will always provide a constant current that is a predefined function of time.
• Symbol is a circle with an arrow in it.
• Current sources provide a constant current flow (DC).
• The direction of flow is that of the flow of positive charge. In electric circuits what actually flows are electrons (negatively charged), so negative charge flowing to the left this is equivalent to positive charge flowing to the right.

Question 18

Resistance in Parallel

Answer 18

1/R(total) = 1/R1 + 1/R2 + 1/R3…

Question 19

Current in Parallel

Answer 19

i(Total) = i1 + i2…

Question 20

Voltage in Parallel

Answer 20

U(Total) = U1 = U2…

Question 21

Conductance

Answer 21

• Inverse of resistance, consider how easy it is for
  current to flow.
  G = 1/R
• Where G is conductance, unit of Siemens (S)

Question 22

Potential

Answer 22

• The Voltage at a node.
• Voltage is a difference in the potential.
• Every node has potential.
• Potential field defines how much energy a charge carries.

Question 23

Ground

Answer 23

• A reference for measuring potential, where voltage is 0 volts.

Question 24

Power (P)

Answer 24

• It takes energy to move electrons against an electric field. Unit of Watts
• The higher the potential difference the more power.
• Product of voltage and current
  P = UI
  P = Ri^2
• If you double the current, and the voltage you quadruple the power.
• Sources provide or absorb the power.

Question 25

Loaded Supply

Answer 25

• A real voltage supply has resistance.
  U = U(0) - IR