1. Current electricity mainly studies what kind of electrical situation?
ⓐ. Charges permanently at rest on isolated bodies
ⓑ. Magnetic poles arranged around a current-carrying wire
ⓒ. Light rays bending through transparent materials
ⓓ. Charges moving steadily through conductors
Correct Answer: Charges moving steadily through conductors
Explanation: Current electricity deals with electric charge in motion, especially in closed conducting circuits. In a torch, for example, charges move through the cell, wire, switch, and bulb when the circuit is complete. This is different from electrostatics, where the main focus is on charges at rest and the fields or potentials produced by them. A steady circuit current needs a conducting path and a source such as a cell or battery. The word steady does not mean that charges are motionless; it means that the rate of flow remains constant at a given cross-section.
2. A rubbed plastic comb attracts small paper bits, while a glowing torch has charge flow through a closed circuit. The torch case belongs more directly to current electricity because it involves
ⓐ. continuous charge flow in a circuit
ⓑ. fixed charge distribution only
ⓒ. charge at rest on an insulating surface
ⓓ. electric force without any source of energy
Correct Answer: continuous charge flow in a circuit
Explanation: The rubbed comb is a familiar electrostatic situation because charge remains mainly at rest on the comb. A torch works only when charge flows through the conducting path containing the cell, switch, and bulb. Current electricity focuses on this continuous flow of charge through a complete circuit. The cell supplies energy that maintains potential difference and keeps the charge flow going. Attraction of paper bits shows electric force, but it does not by itself represent a steady circuit current.
3. In a simple circuit containing a cell, switch, connecting wires, and a lamp, the cell primarily serves to
ⓐ. maintain potential difference across the circuit
ⓑ. remove resistance from the lamp
ⓒ. stop the motion of charges in the wire
ⓓ. convert the circuit into an electrostatic arrangement
Correct Answer: maintain potential difference across the circuit
Explanation: A cell is a source of electrical energy in a circuit. It maintains a potential difference between its terminals, and this potential difference drives charge through the external conducting path when the circuit is closed. The lamp does not glow merely because wires are present; a driving potential difference is also needed. The resistance of the lamp is not removed by the cell, because the lamp still opposes current and converts electrical energy into heat and light. Without a maintained \(V\), the charge flow would not continue steadily.
4. A switch in a torch is opened after the torch was glowing. The lamp goes off mainly because
ⓐ. the cell loses all its stored charge instantly
ⓑ. the resistance of the wire becomes exactly zero
ⓒ. the conducting path becomes incomplete
ⓓ. the lamp changes from a conductor into an insulator
Correct Answer: the conducting path becomes incomplete
Explanation: Opening a switch breaks the circuit path. For a steady current to flow, charges must have a complete conducting path around the circuit. The cell may still have energy, but the open gap prevents continuous charge flow through the lamp. The lamp does not need to become an insulator for the current to stop; breaking the path is enough. In a simple circuit, the switch controls current by completing or interrupting the conducting path.
5. Match the circuit part with its usual role in a simple closed circuit.
| Part | Role |
|---|
| P. Cell | 1. Opens or closes the conducting path |
| Q. Switch | 2. Provides energy and maintains potential difference |
| R. Connecting wire | 3. Offers a path for charge flow |
| S. Lamp | 4. Converts electrical energy into light and heat |
ⓐ. P-2, Q-1, R-3, S-4
ⓑ. P-1, Q-2, R-3, S-4
ⓒ. P-2, Q-3, R-1, S-4
ⓓ. P-3, Q-1, R-2, S-4
Correct Answer: P-2, Q-1, R-3, S-4
Explanation: The cell is the energy source and maintains potential difference between its terminals. The switch controls the circuit by opening or closing the conducting path. Connecting wires provide low-resistance paths for charge flow between circuit elements. The lamp is a device that converts electrical energy mainly into light and heat. These roles are different, so replacing a cell by a switch or a wire by a lamp would change the physical function of the circuit.
6. A heater connected to a battery becomes warm when the circuit is closed. This is a current-electricity situation because
ⓐ. charges remain at rest on the heater surface
ⓑ. the battery only produces attraction between neutral objects
ⓒ. no potential difference is required once the wire is connected
ⓓ. electrical energy is transferred through moving charge
Correct Answer: electrical energy is transferred through moving charge
Explanation: A heater warms because current flows through its resistive element and electrical energy is converted into heat. This requires moving charge in a closed conducting path. The battery maintains the potential difference needed to drive that current. The situation is not only about static attraction between charged and neutral objects. The heating effect belongs naturally to current electricity because energy transfer occurs with continuous charge flow.
7. A circuit is made using only a lamp and a single piece of wire, with no cell or battery connected. The lamp does not glow because the arrangement lacks
ⓐ. a visible metallic part in the lamp
ⓑ. any resistance in the circuit
ⓒ. a maintained potential difference
ⓓ. electrostatic charge on the wire surface
Correct Answer: a maintained potential difference
Explanation: A lamp needs current through its filament or conducting part to glow. A closed conducting path alone is not enough if there is no source to maintain potential difference. A cell or battery supplies energy and keeps the charge flow going through the circuit. The lamp has resistance, and that resistance helps convert electrical energy into heat and light when current flows. Static charge on a wire surface cannot replace a maintained circuit voltage.
8. The pair that best represents one current-electricity example and one electrostatics example, respectively, is
ⓐ. charged comb attracting paper bits; torch bulb glowing
ⓑ. torch bulb glowing; charged comb attracting paper bits
ⓒ. isolated charged sphere; charged comb attracting paper bits
ⓓ. open switch in a dead circuit; isolated neutral rod
Correct Answer: torch bulb glowing; charged comb attracting paper bits
Explanation: A glowing torch bulb is a current-electricity example because charge flows continuously through a closed circuit. A charged comb attracting paper bits is an electrostatics example because it mainly involves charges at rest and the forces caused by them. The order matters here because the first example must involve current electricity. An isolated charged sphere may be charged, but without steady charge flow it is not the main model for current electricity. The clearest distinction is moving charge in a circuit versus stationary charge producing electrostatic effects.
9. In circuit notation, the quantity \(q\) usually represents charge. Its SI unit is
ⓐ. \(\text{A}\)
ⓑ. \(\text{C}\)
ⓒ. \(\Omega\)
ⓓ. \(\text{V}\)
Correct Answer: \(\text{C}\)
Explanation: The symbol \(q\) denotes electric charge in circuit problems. The SI unit of charge is the coulomb, written as \(\text{C}\). The ampere \(\text{A}\) is the unit of current, not charge. The volt \(\text{V}\) is the unit of potential difference, and \(\Omega\) is the unit of resistance. Keeping \(q\) and \(I\) separate is important because current describes how fast charge flows.
10. Study the quantity-unit pairs below and choose the fully matched row.
| Row | Quantity | SI unit |
|---|
| P | Current \(I\) | \(\text{A}\) |
| Q | Potential difference \(V\) | \(\Omega\) |
| R | Resistance \(R\) | \(\text{V}\) |
| S | Energy \(W\) | \(\text{J}\) |
ⓐ. Rows Q and R only
ⓑ. Rows P, Q, and S only
ⓒ. Rows P, R, and S only
ⓓ. Rows P and S only
Correct Answer: Rows P and S only
Explanation: Current \(I\) is measured in ampere \(\text{A}\), so row P is matched properly. Energy \(W\) is measured in joule \(\text{J}\), so row S is also matched properly. Potential difference \(V\) is measured in volt \(\text{V}\), not \(\Omega\). Resistance \(R\) is measured in ohm \(\Omega\), not volt. The symbols \(V\) and \(R\) often appear together in \(V=IR\), but their units must not be interchanged.
11. The unit relation for resistance is \(1\,\Omega =\) ______.
ⓐ. \(1\,\text{A V}^{-1}\)
ⓑ. \(1\,\text{C s}^{-1}\)
ⓒ. \(1\,\text{J C}^{-1}\)
ⓓ. \(1\,\text{V A}^{-1}\)
Correct Answer: \(1\,\text{V A}^{-1}\)
Explanation: Resistance is defined through the relation \(R=\frac{V}{I}\) when Ohm's law is applicable. Therefore, the unit of resistance is the unit of potential difference divided by the unit of current. This gives \(\Omega=\text{V A}^{-1}\). The unit \(\text{A V}^{-1}\) is the reciprocal unit and is related to conductance, not resistance. The relation \(1\,\text{J C}^{-1}=1\,\text{V}\) belongs to potential difference, so it should not be confused with the ohm.
12. A beginner writes \(P\), \(W\), and \(R\) beside three circuit quantities: power, energy, and resistance. The most suitable matching is
ⓐ. \(P\) for energy, \(W\) for resistance, \(R\) for power
ⓑ. \(P\) for power, \(W\) for energy, \(R\) for resistance
ⓒ. \(P\) for resistance, \(W\) for power, \(R\) for energy
ⓓ. \(P\) for resistance, \(W\) for energy, \(R\) for power
Correct Answer: \(P\) for power, \(W\) for energy, \(R\) for resistance
Explanation: In current electricity, \(P\) commonly denotes electric power. The symbol \(W\) is often used for electrical work or energy, while its SI unit is joule \(\text{J}\). Resistance is denoted by \(R\) and measured in ohm \(\Omega\). A possible confusion is that \(\text{W}\) is also the unit symbol for watt, but in formulas \(W\) may represent work or energy. The meaning of a symbol must be read from the physical quantity being discussed, not from the letter alone.
13. A circuit element has resistance \(R\), potential difference \(V\), and current \(I\). The basic algebraic relation that connects these three quantities for an ohmic element under constant physical conditions is
ⓐ. \(I=VR\)
ⓑ. \(V=IR\)
ⓒ. \(R=VI\)
ⓓ. \(V=\frac{I}{R}\)
Correct Answer: \(V=IR\)
Explanation: For an ohmic conductor under constant physical conditions, potential difference is proportional to current. The proportionality relation is written as \(V=IR\), where \(R\) is the resistance. The alternatives \(I=VR\) and \(R=VI\) do not have the right unit structure for Ohm's law. Writing \(V=\frac{I}{R}\) reverses the role of resistance and would imply that larger resistance gives smaller voltage for the same current, opposite to \(V=IR\). The condition of constant physical conditions matters because temperature changes can change the resistance.
14. A small lamp is marked \(6\,\text{V}\) and \(3\,\text{W}\). In this marking, \(3\,\text{W}\) refers to
ⓐ. the charge stored in the lamp
ⓑ. the resistance of the lamp in ohm
ⓒ. the potential difference across each wire
ⓓ. the energy used per unit time
Correct Answer: the energy used per unit time
Explanation: The watt \(\text{W}\) is the SI unit of power. Electric power tells how fast electrical energy is converted into another form, such as light and heat in a lamp. A marking of \(3\,\text{W}\) means the lamp converts \(3\,\text{J}\) of energy each second under its rated operating condition. It is not the amount of charge stored in the lamp, and it is not the resistance unit. The symbol \(\text{W}\) as a unit of power must be distinguished from \(W\) used as a symbol for work or energy.
15. Two identical lamps are connected one after another in a single path with a cell and a switch. This arrangement is best described as a series path because
ⓐ. each lamp is connected directly across the cell separately
ⓑ. the current has only one route through both lamps
ⓒ. the potential difference across every lamp must be zero
ⓓ. the circuit can work even if the path is broken between the lamps
Correct Answer: the current has only one route through both lamps
Explanation: In a series arrangement, circuit elements are connected along a single conducting path. The same current passes through each element because there is no branch where the current can split. If the path is broken at any point, current stops everywhere in that series path. A parallel arrangement is different because each branch gives a separate route between the same two junctions. The phrase one after another is a helpful clue, but the real circuit idea is the single route for charge flow.
16. Two lamps are connected so that each lamp is joined directly across the same two terminals of a cell. The arrangement is parallel because
ⓐ. each lamp has the same potential difference across it
ⓑ. the lamps must carry exactly the same current in all cases
ⓒ. the total resistance must be larger than either lamp resistance
ⓓ. current is forced to pass through one lamp before the other
Correct Answer: each lamp has the same potential difference across it
Explanation: In a parallel arrangement, each branch is connected across the same two junctions. Because the branch ends are the same pair of points, the potential difference across each branch is the same. The current may divide between the branches depending on their resistances, so equal current is not guaranteed unless the branches are identical. A larger equivalent resistance is a feature of series connection, not parallel connection. The defining idea of parallel paths is shared voltage with separate routes for current.
17. Electric current through a wire is defined as the
ⓐ. total charge present inside the wire at one instant
ⓑ. force experienced by each free electron in the wire
ⓒ. rate at which charge flows through a cross-section
ⓓ. energy supplied by the cell per unit charge
Correct Answer: rate at which charge flows through a cross-section
Explanation: Electric current describes how fast charge crosses a chosen cross-section of a conductor. If a charge \(dq\) passes in a small time \(dt\), the instantaneous current is \(I=\frac{dq}{dt}\). The total charge inside the wire is not the current, because current depends on flow rate. Energy per unit charge is potential difference, not current. A wire may contain many free electrons, but current is measured by the charge crossing a section per unit time.
18. If a charge of \(24\,\text{C}\) passes through a cross-section of a conductor in \(8\,\text{s}\), the average current is
ⓐ. \(2\,\text{A}\)
ⓑ. \(16\,\text{A}\)
ⓒ. \(3\,\text{A}\)
ⓓ. \(32\,\text{A}\)
Correct Answer: \(3\,\text{A}\)
Explanation: \( \textbf{Given data:} \) Total charge crossing the section is \(\Delta q=24\,\text{C}\).
\( \textbf{Time interval:} \) \(\Delta t=8\,\text{s}\).
\( \textbf{Required quantity:} \) Average current \(I_{\text{av}}\).
\( \textbf{Useful relation:} \)
\[
I_{\text{av}}=\frac{\Delta q}{\Delta t}
\]
This relation applies because average current is charge flow per unit time over the whole interval.
\( \textbf{Substitution:} \)
\[
I_{\text{av}}=\frac{24\,\text{C}}{8\,\text{s}}
\]
\( \textbf{Calculation:} \)
\[
I_{\text{av}}=3\,\text{C s}^{-1}
\]
Since \(1\,\text{A}=1\,\text{C s}^{-1}\), the value becomes \(3\,\text{A}\).
\( \textbf{Final answer:} \) The average current is \(3\,\text{A}\).
19. In a metallic wire connected to a cell, conventional current is taken in the direction of
ⓐ. positive charge flow
ⓑ. electron drift
ⓒ. negative charge flow
ⓓ. random thermal motion of electrons
Correct Answer: positive charge flow
Explanation: Conventional current is defined as the direction in which positive charge would flow. In a metallic conductor, the mobile charge carriers are electrons, so their drift direction is opposite to conventional current. Random thermal motion of electrons exists even without an applied electric field, but it does not decide the conventional current direction. The cell establishes an electric field that gives electrons a small drift opposite to the field direction. The current direction used in circuit diagrams follows the positive-charge convention even when the actual carriers are electrons.
20. The unit statement \(1\,\text{A}=1\,\text{C s}^{-1}\) means that a current of \(1\,\text{A}\) corresponds to
ⓐ. \(1\,\text{J}\) of energy used in \(1\,\text{s}\)
ⓑ. \(1\,\text{V}\) of potential difference per coulomb
ⓒ. \(1\,\text{C}\) of charge flowing in \(1\,\text{s}\)
ⓓ. \(1\,\Omega\) of resistance per second
Correct Answer: \(1\,\text{C}\) of charge flowing in \(1\,\text{s}\)
Explanation: The ampere is the SI unit of electric current. Since current is the rate of charge flow, \(I=\frac{\Delta q}{\Delta t}\). The unit \(\text{C s}^{-1}\) means coulomb per second. Therefore, \(1\,\text{A}\) represents a flow rate of \(1\,\text{C}\) in every \(1\,\text{s}\). Energy per second is power and is measured in watt \(\text{W}\), so it should not be mixed with current.
