4A4 Simple and Combination Circuits

Question 1

Define:

Electric circuit

Answer 1

A closed loop of electric elements where electric charges flow.

It has a source of electric charges that carry electric potential energy to other circuit components.

Question 2

What are the four main components of a basic electric circuit?

Answer 2

• Power source (AC or DC)
• Load (such as a light bulb)
• Conductive path (wires)
• Switch

Additional components like resistors and capacitors can control current and voltage.

Question 3

What is the function of a load in an electric circuit?

Answer 3

Converts electric potential energy to another form, such as light, heat, or mechanical motion.

Examples include bulbs, resistors, capacitors, and inductors.

Question 4

Define:

EMF

Electromotive Force

Answer 4

Energy supplied per unit charge by a power source; measured in volts (V).
## Footnote

It’s the maximum voltage of a source when no current flows—the open-circuit potential.

Question 5

Fill in the blanks:

In a circuit, the conventional current flows from the ______ terminal to the ______ terminal of the power source.

Answer 5

positive; negative

Conventional current assumes the flow of positive charges, even though electrons actually move in the opposite direction.

Question 6

What happens in a series circuit when one component fails?

Answer 6

The circuit is opened and cannot work.

This occurs because the components are connected like a chain.

Question 7

Define:

Series circuit

Answer 7

A circuit in which components are connected end-to-end, providing a single path for current.

In series circuits, the current is the same through all components, but the voltage divides.

Question 8

Define:

Parallel circuit

Answer 8

A circuit in which multiple paths are available for current to flow.

Each component is connected across the same two points of the circuit.

Question 9

True or false:

In a parallel circuit, the voltage is the same across all branches.

Answer 9

True

The voltage remains constant across all parallel components, but the current divides.

Question 10

Explain why combination circuits are useful in practical applications.

Answer 10

They combine series and parallel circuits, allowing control over both current and voltage.

These circuits are used in systems like home wiring, where some parts need shared current (series) and others need independent paths (parallel).

Question 11

In a series circuit, how does adding a component affect the total resistance?

Answer 11

It increases the total resistance of the circuit.

This causes the total voltage to be more divided among the components.

Question 12

What type of circuit is most common in home electrical systems?

Answer 12

Parallel circuit

Parallel circuits ensure that each device receives the same voltage and can operate independently.

Question 13

What happens to the current if one resistor fails in a series circuit with three resistors?

Answer 13

The current stops flowing.

In a series circuit, any break stops the entire current because there’s only one path.

Question 14

What happens when you remove a bulb from a parallel circuit?

Answer 14

The total resistance increases, and total current decreases.

However, the remaining bulbs still receive the full voltage.

Question 15

How is current affected in a parallel circuit when more branches are added?

Answer 15

The total current increases.

This occurs because the circuit’s overall resistance decreases as more parallel paths are added.

Question 16

True or false:

Series circuits are more energy-efficient than parallel circuits.

Answer 16

False

Parallel circuits are often more energy-efficient and practical for distributing power in systems.

Question 17

Why do Christmas lights often use parallel circuits instead of series circuits?

Answer 17

If one bulb burns out, the others remain lit.

In parallel circuits, each bulb has an independent connection to the power source.

Question 18

How does Ohm’s Law apply to a series circuit?

Answer 18

Ohm’s Law can determine the total resistance by adding individual resistances.

In a series circuit, the current is the same throughout. The total voltage is divided among the components based on their resistances.

Question 19

Explain how Ohm’s Law applies to a parallel circuit.

Answer 19

Ohm’s Law can be applied to each branch individually because the voltage across each branch is the same.

The total current is the sum of the currents through each branch.

Question 20

Define:

Equivalent resistance

Answer 20

Single resistance that could replace all resistors in a circuit without changing the total current or voltage.

It depends on whether it is a parallel or series circuit.

Question 21

How do you find the equivalent resistance in a series circuit?

Answer 21

Sum the individual resistances:
Req =R1+R2+R3+…

The same current flows through all resistors in a series circuit.

Question 22

How do you find the equivalent resistance in a parallel circuit?

Answer 22

Sum of the reciprocal individual resistances:
1/Req = 1/R1 + 1/R2 + 1/R3 + ⋯

The voltage across each resistor is the same in a parallel circuit.

Question 23

True or false:

Adding more resistors in parallel reduces the total resistance.

Answer 23

True

This happens because more pathways for current are created.

Question 24

A circuit has three resistors: 4Ω, 6Ω, and 8Ω connected in series. What is the total resistance?

Answer 24

18Ω

4Ω+6Ω+8Ω=18Ω

Question 25

# True or false: The **equivalent resistance in series** is always greater than any individual resistance.

Answer 25

True ## Footnote This follows directly from the sum rule of resistances.

Question 26

# Define: Equivalent capacitance

Answer 26

Single capacitance that **could replace multiple capacitors** in a circuit while maintaining the same electrical behavior. ## Footnote It depends on whether it is a parallel or series circuit.

Question 27

What happens to **equivalent capacitance** when capacitors are placed in **parallel**?

Answer 27

The equivalent capacitance increases. ## Footnote This is because the equivalent capacitance is the sum of the individual capacitances.

Question 28

What is the formula for **equivalent capacitance in parallel**?

Answer 28

Ceq = C1 + C2 + C3 + ⋯ ## Footnote This formula indicates that you sum the capacitances of all capacitors in parallel.

Question 29

# Fill in the blank: In a **series circuit**, the **total capacitance** is \_\_\_\_\_\_ than the smallest individual capacitance.

Answer 29

less ## Footnote In series, 1/Ceq = 1/C1 + 1/C2 + 1/C3 + ⋯

Question 30

How do you find the **equivalent capacitance** of a **complex circuit**?

Answer 30

1. Find the equivalent capacitances of isolated pieces of the circuit. 2. Redraw the circuit with new equivalent capacitors. 3. Repeat until a single capacitor is obtained. ## Footnote This method allows for systematic simplification of complex circuits.

Question 31

What happens to **equivalent capacitance** when capacitors are placed in **series**?

Answer 31

The equivalent capacitance **decreases**. ## Footnote In series, the equivalent capacitance is less than the smallest individual capacitance.

Question 32

What is the effect of adding **capacitors in parallel** on the total capacitance?

Answer 32

It **increases** compared to individual capacitances. ## Footnote For example, three capacitors with capacitances of 10μF, 3μF, and 8μF yield an equivalent capacitance of 21μF.

Question 33

What is the effect of adding **capacitors in series** on the total capacitance?

Answer 33

It **decreases** compared to individual capacitances. ## Footnote For instance, three capacitors with capacitances of 10μF, 3μF, and 8μF yield an equivalent capacitance of approximately 1.79μF.

Question 34

Explain why **equivalent capacitance** is lower in series than in parallel.

Answer 34

In series, the **effective separation** between capacitor plates increases, lowering total capacitance. ## Footnote In parallel, the effective plate area increases, boosting capacitance.

Question 35

Explain why **capacitors** are often connected in parallel in **power supply circuits**.

Answer 35

To **store more charge** and provide a stable voltage. ## Footnote Higher capacitance in parallel improves filtering in power supplies.

Question 36

If two 10 μF capacitors are connected in series, what is their **equivalent capacitance**?

Answer 36

5 μF ## Footnote 1/Ceq = 1/10μF + 1/10μF

Question 37

Why are capacitors ideal for use in **timing circuits**?

Answer 37

They store and release charge at **predictable rates**. ## Footnote This property allows capacitors to control timing intervals.

Question 38

# Define: Kirchhoff's Current Law (KCL)

Answer 38

The total current entering a junction **must equal** the total current leaving a junction. ## Footnote This law is based on the conservation of electric charge.

Question 39

# Define: Kirchhoff's Voltage Law | (KVL)

Answer 39

The **change in potential** around a closed loop must be **zero**. ## Footnote This law is derived from the conservation of energy.

Question 40

# True or false **Kirchhoff's Voltage Law** applies only to series circuits.

Answer 40

False ## Footnote KVL applies to any closed loop, regardless of circuit configuration.

Question 41

# Define: Nodes | in Kirchhoff's laws

Answer 41

They are **connections** of two or more current-carrying routes. ## Footnote Kirchhoff's laws apply to these junction points in circuits.

Question 42

What is the first step in **solving problems** using **Kirchhoff's laws**?

Answer 42

**Label the current** in each branch of the circuit and label the direction. ## Footnote This helps in identifying unknowns and applying the laws correctly.

Question 43

What are the **limitations of Kirchhoff's circuit laws**?

Answer 43

They **lose validity in high-frequency** AC circuits. ## Footnote The laws depend on assumptions about constant net charge and stable magnetic fields, which may not hold in such cases.

Question 44

Explain why **KCL** is useful when analyzing **complex circuits**.

Answer 44

It helps **determine the current** at each junction. ## Footnote KCL simplifies current distribution analysis in circuits.

Question 45

What does **Kirchhoff's Voltage Law** imply about **potential differences** in a closed loop?

Answer 45

They **cancel each other** out to zero. ## Footnote The total energy gained equals the total energy lost.

Question 46

# True or false: **Kirchhoff's Voltage Law** can be applied to analyze circuits with **multiple power sources**.

Answer 46

True ## Footnote KVL is valid regardless of the number of power sources in the loop, as long as all voltage gains and drops are accounted for.

Question 47

If I₁ flows into a junction and I₂ and I₃ flow out, how is **Kirchhoff’s Current Law** expressed?

Answer 47

I₁ = I₂ + I₃ ## Footnote Based on charge conservation: total inflow = outflow at a junction.

Question 48

Why is KVL essential in **power distribution networks**?

Answer 48

It ensures that **voltage levels are consistent** and manageable. ## Footnote This prevents voltage imbalances and ensures circuit stability.

Question 49

# True or false: **KCL** states that current can accumulate at a junction.

Answer 49

False ## Footnote Current cannot accumulate due to charge conservation.

Question 50

How does **KCL** apply to **parallel circuits**?

Answer 50

The **sum of currents** through each branch equals the total current entering the circuit. ## Footnote Each branch carries part of the total current.

Question 51

# True or false: **Power** is inversely proportional to **voltage**.

Answer 51

False ## Footnote Power increases with voltage if current is constant.

Question 52

Explain why **power transmission lines** use high voltage.

Answer 52

To **reduce current** and **minimize power loss** due to resistance. ## Footnote Lower current reduces resistive heating losses.

Question 53

What is the difference between **real power** and **reactive power**?

Answer 53

* Real power does **useful work**. * Reactive power **maintains voltage levels** in AC systems. ## Footnote Real power is measured in watts; reactive power in VARs (volt-ampere reactive).

Question 54

How is **power** calculated in a **series circuit**?

Answer 54

It is calculated as **P=I²R,** where the current is constant throughout the circuit, and the total resistance is the sum of individual resistances. ## Footnote The total power is the sum of the power dissipated in each resistor.

Question 55

# True or false: In a **parallel circuit**, the **total power** is the sum of the power consumed by each branch.

Answer 55

True ## Footnote Each branch operates independently with the same voltage across them.

Question 56

# Fill in the blank: In a \_\_\_\_\_\_ circuit, the **power dissipated** by each resistor can be calculated as P=V²/R, where voltage across each branch is the same.

Answer 56

parallel ## Footnote Power dissipation in each branch depends on the resistance.

Question 57

# True or false: A **100-watt bulb** uses more energy in one second than a **60-watt bulb**.

Answer 57

True ## Footnote Higher power ratings consume energy faster.