Electric Current and Circuits

Question 1

What is the formal definition of electric current?

Accepted Answer

The rate at which charge flows: $I = \frac{\Delta Q}{\Delta t}$

Question 2

What is the SI unit for current, and how is it defined in base units?

Accepted Answer

Ampere (A); one coulomb per second (1 C/s)

Question 3

By convention, what is the defined direction of electric current flow?

Accepted Answer

The direction in which positive charge would flow

Question 4

In a common metal wire, which particles actually move to carry the current?

Accepted Answer

Electrons (negative charges)

Question 5

How does the speed of an electrical signal compare to the drift velocity of individual electrons?

Accepted Answer

Signal speed is near light speed; drift velocity is very slow

Question 6

According to Ohm’s law, what is the relationship between current and applied voltage?

Accepted Answer

Current is directly proportional to voltage ($I \propto V$)

Question 7

What is the defining characteristic of an "ohmic" material?

Accepted Answer

Resistance remains constant regardless of voltage or current

Question 8

Electric Current — What is the unit for resistance?

Accepted Answer

Ohm ($\Omega$), equivalent to 1 Volt per Ampere

Question 9

What happens to the current in a circuit if the resistance is doubled while voltage remains constant?

Accepted Answer

The current is cut in half

Question 10

How does increasing the length (L) of a wire affect its electrical resistance?

Accepted Answer

Resistance increases proportionally with length

Question 11

How does increasing the cross-sectional area (A) of a conductor affect its resistance?

Accepted Answer

Resistance decreases (inversely proportional to area)

Question 12

What is the difference between resistance and resistivity?

Accepted Answer

Resistivity is an intrinsic material property; resistance depends on shape

Question 13

Which equation relates resistance to resistivity, length, and area?

Accepted Answer

$$R = \frac{\rho L}{A}$$

Question 14

How does the resistance of most metals change as their temperature increases?

Accepted Answer

Resistance increases because atoms vibrate more, causing more collisions

Question 15

What does a negative temperature coefficient of resistivity ($\alpha < 0$) imply for a material?

Accepted Answer

Resistivity decreases as temperature increases (common in semiconductors)

Question 16

What is the formula for the total resistance ($R_s$) of resistors connected in series?

Accepted Answer

$$R_s = R_1 + R_2 + R_3 + \dots$$

Question 17

In a series circuit, which electrical quantity is identical across all resistors?

Accepted Answer

Current ($I$)

Question 18

How is the total resistance ($R_p$) calculated for a parallel circuit?

Accepted Answer

$$\frac{1}{R_p} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3} + \dots$$

Question 19

In a parallel circuit, which electrical quantity is identical across all branches?

Accepted Answer

Voltage ($V$)

Question 20

Total resistance in a parallel circuit is always ________ than the smallest individual resistor.

Accepted Answer

Less

Question 21

What does "electromotive force" (emf) represent?

Accepted Answer

The potential difference of a source when no current flows

Question 22

Why is the terminal voltage of a battery usually lower than its emf?

Accepted Answer

Voltage is lost due to the battery's internal resistance ($Ir$)

Question 23

Which equation calculates the terminal voltage (V) of a power source?

Accepted Answer

$$V = \text{emf} - Ir$$

Question 24

What typically happens to a battery's internal resistance as it becomes depleted?

Accepted Answer

Internal resistance increases

Question 25

What is the physical meaning of an "IR drop"?

Accepted Answer

The voltage decrease across a resistor caused by current flow