Chapter 10 #2

Question 1

Question:

Answer 1

Answer:

Question 2

Section 1: Properties of Electric Charge

Question 3

What are the two types of electric charges and how do they interact?

Answer 3

There are positive and negative charges. Like charges repel each other, while unlike charges attract.

Question 4

What is the principle of conservation of charge?

Answer 4

Charge is conserved; if a body loses charge, another must gain the same amount. The net charge of an isolated system remains constant.

Question 5

What does it mean that electric charge is “quantized”?

Answer 5

Any charge carried by a body must be an integer multiple of the elementary charge carried by an electron (e = 1.602 × 10^{-19} C).

Question 6

Section 2: Electric Current and Charge

Question 7

How is electric current (I) defined?

Answer 7

Electric current is the amount of charge (Q) passing through a wire per unit time (t), expressed as I = Q/t.

Question 8

What is the difference between electron flow and conventional current?

Answer 8

Electrons flow from negative to positive. Conventional current assumes positive charge motion and flows from positive to negative.

Question 9

What is the definition of one Coulomb?

Answer 9

One Coulomb is the amount of charge that flows past a point when a current of one Ampere flows for one second.

Question 10

How can the total charge passing in a circuit be determined from a graph?

Answer 10

The total charge is the area under a current-time (I–t) graph.

Question 11

Section 3: The Equation of Current (I = nAvq)

Question 12

In the formula I = nAvq, what does each symbol represent?

Answer 12

I is current, n is number density of charge carriers (m⁻³), A is cross-sectional area, v is mean drift velocity, and q is the charge of each particle.

Question 13

What is the difference between ‘n’ and ‘N’ in the context of electricity?

Answer 13

‘n’ is the number density of free electrons (electrons per unit volume), while ‘N’ is the total number of free electrons (no units).

Question 14

How do you calculate the total charge (Q) using the number of free electrons (N)?

Answer 14

Q = eN, where e is the elementary charge.

Question 15

If two wires in series have different diameters, how does the drift velocity (v) change?

Answer 15

Drift velocity is inversely proportional to the cross-sectional area (A) and the square of the diameter (d²). If the diameter doubles, drift velocity becomes 1/4 of the original.

Question 16

What is the “mean drift velocity” (v)?

Answer 16

It is the average speed at which charge carriers (like electrons) move through a conductor when a potential difference is applied.

Question 17

Section 4: EMF and Potential Difference

Question 18

Define Electromotive Force (EMF).

Answer 18

EMF is the non-electrical energy (e.g., chemical) converted to electrical energy per unit charge driven through the source.

Question 19

Define Potential Difference (P.D.).

Answer 19

P.D. is the electrical energy converted to other forms of energy (e.g., heat, light) per unit charge passing through a component.

Question 20

What is the formula for calculating P.D. or EMF?

Answer 20

V or E = W/Q, where W is energy (work done) and Q is charge.

Question 21

Define the Volt.

Answer 21

One Volt is the potential difference between two points if one Joule of electrical energy is converted to other forms when one Coulomb of charge passes between them (1 V = 1 J/C).

Question 22

Section 5: Resistance and Ohm’s Law

Question 23

State Ohm’s Law.

Answer 23

At a constant temperature, the potential difference across a conductor is directly proportional to the current passing through it (V ∝ I).

Question 24

What is electrical resistance (R)?

Answer 24

Resistance is the ratio between the potential difference across a conductor and the current passing through it (R = V/I).

Question 25

Define the Ohm (Ω).

Answer 25

One Ohm is the resistance of a conductor when a P.D. of one volt produces a current of one ampere.

Question 26

Why do metals have electrical resistance?

Answer 26

Free electrons collide with the vibrating metal ions in the lattice, which opposes their flow.

Question 27

Section 6: I-V Characteristics

Question 28

How is resistance determined from an I-V characteristic graph?

Answer 28

At any point, resistance R = V/I. Note that the gradient is I/V, so R = 1/gradient.

Question 29

Describe the I-V graph for a filament lamp.

Answer 29

It is a curve because resistance increases as voltage increases (the lamp gets hotter), making it a non-ohmic conductor.

Question 30

Describe the I-V graph for a semiconductor diode.

Answer 30

It allows current in one direction (forward bias) after a certain voltage, but shows zero current in the opposite direction (reverse bias).

Question 31

Section 7: Factors Affecting Resistance and Resistivity

Question 32

What four factors affect the resistance (R) of a wire?

Answer 32

Length (L), cross-sectional area (A), material (resistivity ρ), and temperature.

Question 33

Define Resistivity (ρ).

Answer 33

Resistivity is the resistance of a wire of length 1m and cross-sectional area 1m² at a constant temperature.

Question 34

What is the formula for Resistivity?

Answer 34

ρ = RA/L.

Question 35

How does resistivity differ from resistance?

Answer 35

Resistance depends on the dimensions (length, area) of the wire, whereas resistivity depends only on the material itself.

Question 36

If a wire is stretched so its length triples (3L) and volume remains constant, how does resistance change?

Answer 36

If volume (V = LA) is constant, A = V/L. Substituting this into R = ρL² / V. Thus, R ∝ L². If length triples, resistance increases by 9 times.

Question 37

Section 8: Temperature Effects on Materials

Question 38

How does temperature affect the resistance of a conductor?

Answer 38

Increasing temperature increases the resistance of a conductor.

Question 39

How does temperature affect the resistance of a semiconductor (like a thermistor)?

Answer 39

Increasing temperature decreases the resistance of a semiconductor.

Question 40

What happens to the collisions inside a metal as temperature increases?

Answer 40

Metal ions vibrate more, leading to more frequent collisions with free electrons, which increases resistance.

Question 41

Section 9: Additional Concepts and Calculations

Question 42

Define an Electric Field.

Answer 42

A region where an electrically charged particle experiences an electric force.

Question 43

What is Electric Field Strength (E)?

Answer 43

It is the electric force per unit positive charge (E = F/q) or the P.D. per unit separation of plates (E = V/d).

Question 44

In which direction does an electric force act on a negatively charged particle?

Answer 44

The force acts in the direction opposite to the electric field.

Question 45

What is "short-circuiting"?

Answer 45

When a zero-resistance component is connected in parallel with a resistor, all current passes through the zero-resistance path, and zero current/P.D. exists across the resistor.

Question 46

How do you calculate the rate of flow of electrons?

Answer 46

Rate of flow of electrons = N/t = I/e.

Question 47

What is the formula for Power (P) in a resistor?

Answer 47

P = I²R or P = V²/R.

Question 48

If two resistors X and Y are in series and the voltage across Y decreases, what happens to the voltage across X?

Answer 48

The voltage drop across X increases.