AP Physics: Electric Current, Resistance, and Ohm's Law flashcards

Question 1

What is the rate at which electric charge flows called?

Accepted Answer

Electric current (I = ΔQ/Δt).

Question 2

What is the SI unit of electric current?

Accepted Answer

The ampere (A), also called the amp.

Question 3

One ampere is equal to how much charge per unit time?

Accepted Answer

One coulomb per second.

Question 4

What is the name for current in which charge moves in one direction only?

Accepted Answer

Direct current (DC).

Question 5

What is the name for current in which the charge flow reverses direction at regular intervals?

Accepted Answer

Alternating current (AC).

Question 6

What is the average velocity of free charges flowing in response to an electric field called?

Accepted Answer

Drift velocity.

Question 7

What is the unit of electrical resistance, with the symbol Ω?

Accepted Answer

The ohm.

Question 8

One ohm is the same as one volt divided by which unit?

Accepted Answer

The ampere (1 Ω = 1 V/A).

Question 9

Which empirical relation says current is proportional to the potential difference across a conductor?

Accepted Answer

Ohm's law, often written I = V/R.

Question 10

Is Ohm's law a universally valid law of nature?

Accepted Answer

No. It is an empirical relation that holds for many materials but not all.

Question 11

What is a material called if Ohm's law applies to it?

Accepted Answer

Ohmic.

Question 12

What is the electric property that impedes current?

Accepted Answer

Resistance.

Question 13

For an ohmic material, resistance is equal to which ratio?

Accepted Answer

Voltage divided by current (R = V/I).

Question 14

If the resistance in a circuit doubles while the voltage stays the same, what happens to the current?

Accepted Answer

It is cut in half.

Question 15

What do we call a low-resistance path between the terminals of a voltage source?

Accepted Answer

A short circuit (a "short").

Question 16

What intrinsic property of a material, independent of the object's shape and size, is proportional to the object's resistance?

Accepted Answer

Resistivity.

Question 17

Which Greek letter is the usual symbol for resistivity?

Accepted Answer

Rho (ρ).

Question 18

For a uniform wire, how does resistance change with its length?

Accepted Answer

It is directly proportional to the length.

Question 19

For a uniform wire, how does resistance depend on its cross-sectional area?

Accepted Answer

It is inversely proportional to the area: a thicker wire has less resistance.

Question 20

Which three classes of material are grouped by their resistivity, from smallest to largest?

Accepted Answer

Conductors, semiconductors, insulators.

Question 21

Which class of material has resistivities between those of conductors and insulators?

Accepted Answer

Semiconductors.

Question 22

What empirical quantity, symbol α, describes how a material's resistivity changes with temperature?

Accepted Answer

The temperature coefficient of resistivity.

Question 23

Over modest temperature changes, what happens to the resistivity of a metal as it gets hotter?

Accepted Answer

It increases (α is positive for metals).

Question 24

Over modest temperature changes, what happens to the resistivity of a semiconductor such as silicon as it gets hotter?

Accepted Answer

It decreases (α is negative), because more free charges become available.

Question 25

What is a material called whose resistivity drops to zero at very low temperatures?

Accepted Answer

A superconductor.

Question 26

In which direction does conventional current point?

Accepted Answer

The direction in which positive charge would flow.

Question 27

What carries the current in a metal wire?

Accepted Answer

Free electrons (negative charges).

Question 28

What is the rate at which a source supplies electrical energy, or a device dissipates it, called?

Accepted Answer

Electric power (equal to current times voltage, P = IV).

Question 29

Of the three expressions P = IV, P = I²R and P = V²/R, which is always valid?

Accepted Answer

P = IV. The other two apply only to resistors.

Question 30

What is the unit of power, in terms of joules?

Accepted Answer

The watt: one joule per second.

Question 31

What energy unit appears on household electric bills?

Accepted Answer

The kilowatt-hour (kWh).

Question 32

What does "rms" stand for in rms current and rms voltage?

Accepted Answer

Root mean square.

Question 33

What three steps give a root mean square of a quantity?

Accepted Answer

Square it, find the mean, then take the square root.

Question 34

Why do large power distribution systems mostly use AC?

Accepted Answer

AC voltages are much easier to step up and down than DC voltages.

AP Physics: Electric Current, Resistance, and Ohm's Law flashcards

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