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Quizzes > Science > Physics

Electromotive Force Quiz: How Much Can You Score?

Curious what is electromotive force? Take this free quiz now!

Difficulty: Moderate
2-5mins
Learning OutcomesCheat Sheet
Paper art illustration showing battery resistor lightbulb EMF text on teal background for free electromotive force quiz

Think you know the spark behind every circuit? Whether you're a student or an electricity enthusiast, spark your curiosity with every question. Dive into our Electromotive Force Quiz: Test Your Electricity Knowledge and see why electromotive force is another term for the push that drives current. From defining electromotive force basics and answering what is electromotive force to tackling EMF voltage concepts, you'll tackle essential electricity quiz questions on resistance and voltage. Ready to challenge yourself? Try our emf or potential difference round, sharpen your insights with an electric forces and electric fields quiz . Light up your understanding - start now!

Which of the following best defines electromotive force (EMF)?
The energy dissipated per unit charge in a resistor
The potential difference between two points in a conductor
The current produced by a cell
The work done per unit charge by a source to move charge around a circuit
Electromotive force (EMF) is defined as the work done by a source in moving one coulomb of charge completely around a circuit. It is not a force but an energy per unit charge. EMF represents the maximum potential difference a source can provide when no current flows. More on EMF
What is the SI unit of EMF?
Ohm
Joule
Ampere
Volt
EMF is measured in volts, the same unit as electrical potential difference. One volt equals one joule of work per coulomb of charge. This unit applies to both open-circuit EMF and terminal voltage. Volt unit explained
According to Ohm's law, which formula relates voltage (V), current (I), and resistance (R)?
V = R / I
V = I × R
I = V × R
R = V × I
Ohm's law states that the voltage across a resistor is the product of the current through it and its resistance. This linear relationship holds for ohmic materials under constant temperature. It is fundamental in circuit analysis. Ohm's Law details
What is the difference between EMF and terminal voltage when a current flows in a cell with internal resistance?
Terminal voltage is always greater than EMF
EMF equals terminal voltage plus the external resistance drop
Terminal voltage equals EMF minus the internal voltage drop
They are equal if current flows
When current flows, some of the EMF is lost across the cell's internal resistance, reducing the terminal voltage. Thus the terminal voltage equals EMF minus I×r, where r is the internal resistance. At zero current, terminal voltage equals EMF. Internal resistance explained
In a series connection of two identical cells, each of EMF E and internal resistance r, what is the total EMF and total internal resistance?
Total EMF = 2E, total r = 2r
Total EMF = E, total r = 2r
Total EMF = E/2, total r = 2r
Total EMF = 2E, total r = r
When cells are in series, their EMFs add algebraically and internal resistances add as well. Thus two cells each of EMF E and resistance r give 2E and 2r. Series connection increases voltage but also total internal resistance. Series cells and resistance
Which statement about internal resistance of a cell is correct?
It reduces the terminal voltage when current flows
It increases the EMF under load
It has no effect when current flows
It increases the open-circuit voltage
The internal resistance of a cell causes a voltage drop I×r inside the cell when current flows, reducing the terminal voltage. It does not change the EMF, which is set by the cell's chemistry. At zero current, the terminal voltage equals the EMF. Internal resistance effects
Which law states that the algebraic sum of the potential differences around a closed loop is zero?
Ohm's Law
Kirchhoff's Voltage Law
Coulomb's Law
Faraday's Law
Kirchhoff's Voltage Law (KVL) says that around any closed circuit loop, the sum of voltage rises equals the sum of voltage drops, so the net change is zero. It is based on energy conservation in electrical networks. Kirchhoff's laws
A cell of EMF 12 V and internal resistance 1 ? delivers a current of 2 A. What is its terminal voltage?
14 V
12 V
2 V
10 V
Terminal voltage V = EMF - I·r = 12 V - (2 A×1 ?) = 10 V. The internal resistance causes a drop of 2 V inside the cell. Without current, terminal voltage equals 12 V. Terminal voltage calculation
What are 'lost volts' in the context of a practical cell?
Voltage due to emf
Voltage drop across internal resistance
Voltage across external resistor
Voltage lost in wiring
Lost volts refer to the internal voltage drop I·r within a cell when it supplies current. They represent the difference between the EMF and the terminal voltage under load. Lost volts increase with current. Lost volts explained
Two identical cells, each of EMF E and resistance r, are connected in parallel. What is the equivalent EMF and internal resistance?
EMF = E, r_eq = 2r
EMF = 2E, r_eq = r/2
EMF = 2E, r_eq = 2r
EMF = E, r_eq = r/2
In parallel, EMFs of identical ideal sources remain E, while internal resistances combine like parallel resistors: r_eq = r/2. This arrangement delivers higher current with lower effective resistance. Parallel cells
How is the efficiency ? of a cell under load defined?
? = (terminal voltage / EMF) × 100%
? = I^2R / EMF
? = (EMF / terminal voltage) × 100%
? = EMF - terminal voltage
Efficiency is the ratio of useful voltage output (terminal voltage) to input EMF, times 100%. It quantifies how much of the chemical energy appears as electrical energy in the external circuit. Losses occur as I·r internally. Cell efficiency
In a potential divider circuit with two resistors R1 and R2 across EMF E, what is the voltage across R2?
E / (R1 + R2)
E × (R1 + R2) / R2
E × R1 / (R1 + R2)
E × R2 / (R1 + R2)
A potential divider divides EMF in proportion to resistances. The voltage across R2 is E·R2/(R1+R2). This assumes negligible loading on the divider. Voltage divider rule
A cell with EMF 9 V and internal resistance 0.5 ? is connected to a load and delivers 3 A. What is its lost volts?
27 V
4.5 V
3 V
1.5 V
Lost volts = I·r = 3 A × 0.5 ? = 1.5 V. These volts are dropped across the internal resistance and do not appear at the terminals. Calculating lost volts
Which orientation of a cell and resistor yields maximum terminal voltage for a given EMF?
Series with infinite resistance
No current drawn (open circuit)
Maximum current load
Short-circuited
When no current is drawn, there is no internal voltage drop (I·r = 0), so terminal voltage equals the full EMF. Any load drawing current reduces terminal voltage. Open-circuit voltage
For maximum power transfer from a cell of EMF E and internal resistance r to a load R, what must be true?
R = r
R = 2r
R = E/r
R = r/2
Maximum power transfer occurs when the load resistance equals the internal resistance of the source (R = r). Under this condition, half of the power is dissipated in the load. This theorem is fundamental in circuit and network design. Maximum power transfer theorem
A rod of length L moves at velocity v perpendicular to a uniform magnetic field B. What is the motional EMF induced between its ends?
E = B·v / L
E = B·L·v
E = B / (L·v)
E = L·v / B
Motional EMF is given by E = B·L·v when a conductor of length L moves at speed v perpendicular to a magnetic field B. Charges experience magnetic force and accumulate at ends, creating potential difference. Motional EMF
According to Faraday's law, the induced EMF in a loop equals:
Rate of change of electric flux
Magnetic field strength times area
Product of current and resistance
Negative rate of change of magnetic flux through the loop
Faraday's law states ? = -d?B/dt, where ?B is the magnetic flux through the loop. The negative sign indicates Lenz's law, opposing the change. It underpins generators and transformers. Faraday's law
Which statement describes Lenz's law in electromagnetic induction?
Induced current always increases the original flux
Induced EMF is proportional to the external circuit resistance
Induced EMF is independent of the direction of motion
Induced EMF produces a current whose magnetic field opposes the change in flux
Lenz's law states that the direction of induced current is such that it opposes the change in magnetic flux that produced it. This is represented by the negative sign in Faraday's law. It ensures conservation of energy. Lenz's law
In an RC circuit with EMF E, resistor R and capacitor C initially uncharged, what is the time constant ??
C / R
R × C
R / C
E / (R·C)
The time constant ? for charging or discharging in an RC circuit is ? = R·C. It characterizes the exponential rate at which the capacitor charges to about 63% of EMF. This arises from solving the differential equation. RC circuit time constant
How does temperature generally affect the internal resistance of a typical chemical cell?
Resistance is independent of temperature
Resistance decreases as temperature increases
Resistance increases as temperature increases
Resistance oscillates with temperature
Chemical cells usually have lower internal resistance at higher temperatures due to increased ion mobility in the electrolyte. Conversely, low temperatures increase resistance and reduce performance. Temperature effects on batteries
A single-turn coil of area 0.1 m² is in a magnetic field dropping uniformly from 2 T to 0 T in 0.5 s. What is the magnitude of the induced EMF?
4 V
2 V
0.04 V
0.4 V
Faraday's law gives ? = |??/?t| = |(B·A)/t| = (2 T×0.1 m²)/0.5 s = 0.4 V. The coil has one turn so no multiplication needed. Induced EMF example
In a series circuit, two cells of EMFs 5 V and 3 V with internal resistances 1 ? and 2 ? are connected. What is the net EMF and total internal resistance?
EMF = 2 V, r = 1 ?
EMF = 8 V, r = 2 ?
EMF = 2 V, r = 3 ?
EMF = 8 V, r = 3 ?
In series, EMFs add algebraically (5 V + 3 V = 8 V) and internal resistances add (1 ? + 2 ? = 3 ?). This yields a combined source with higher voltage and cumulative resistance. Series cell sums
A circuit has self-inductance L. If the current through it changes at rate di/dt, what EMF is induced opposing the change?
? = (di/dt) / L
? = -L / (di/dt)
? = -L (di/dt)
? = L (di/dt)
Self-induced EMF in an inductor is ? = -L·(di/dt), with the negative sign indicating opposition to the change in current (Lenz's law). This relation defines the inductor's behavior in transient circuits. Self-inductance
A conducting loop rotates with angular speed ? in a non-uniform magnetic field B(r). Which integral expression gives the instantaneous EMF?
? = -d/dt ? B·dA
? = -? J·dA
? = ? E·dl
? = ? B·dl
Faraday's law in integral form is ? = -d/dt ?(B·dA) over the loop's area. For a rotating loop in non-uniform B, one must evaluate the time derivative of the flux integral. Faraday's integral form
In a two-loop circuit, cell A (EMF E?, r?) and cell B (EMF E?, r?) share a common resistor R. Which method would you use to find the current in each loop?
Use Faraday's law directly
Assume currents are equal and divide total EMF by total resistance
Apply Kirchhoff's loop and junction rules to form simultaneous equations
Use only Ohm's law on each branch independently
For multi-loop circuits with multiple EMFs, Kirchhoff's voltage and current laws allow writing simultaneous equations for each loop and junction. Solutions give currents and voltages throughout the network. Multi-loop analysis
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Study Outcomes

  1. Define Electromotive Force -

    Understand what is electromotive force and recognize that electromotive force is another term for voltage that drives current in a circuit.

  2. Differentiate EMF and Terminal Voltage -

    Analyze the distinction between electromotive force and terminal voltage to clarify how potential differences affect circuit performance.

  3. Apply Ohm's Law Effectively -

    Calculate current, resistance, and EMF values in simple circuits using Ohm's Law and reinforce your problem-solving skills.

  4. Analyze Circuit Fundamentals -

    Interpret basic circuit diagrams to identify how voltage sources, resistors, and conductors interact under various conditions.

  5. Evaluate EMF Voltage Concepts -

    Assess various EMF voltage concepts through targeted electricity quiz questions to deepen your understanding of voltage behavior.

  6. Identify EMF Sources in Practical Scenarios -

    Recognize common sources of electromotive force in real-world applications and predict their impact on overall circuit operation.

Cheat Sheet

  1. Definition of Electromotive Force -

    Electromotive force is another term for the energy per unit charge developed by any source, and to define electromotive force in simple terms, use ε=W/q. This concept answers what is electromotive force in many introductory texts and sets the stage for understanding voltage sources. As a mnemonic, "Battery Gives Energy" reminds you that a source supplies energy to charges.

  2. EMF vs Terminal Voltage -

    Internal resistance in a battery causes its terminal voltage V to drop under load, following the EMF voltage concepts formula V = ε - Ir, where I is current and r is internal resistance. This distinction fills common electricity quiz questions asking you to differentiate open-circuit EMF and loaded voltage. Practice by plugging different I values to see how V decreases with heavier loads.

  3. Faraday's Law of Induction -

    Faraday's law quantifies induced EMF as ε = - dΦ/dt, where Φ is magnetic flux through a loop; many electricity quiz questions on what is electromotive force rely on this relation. It explains how changing magnetic fields in generators and transformers create voltage. Remember "Flux Falls Fast" to recall that a rapid flux change induces higher EMF.

  4. Kirchhoff's Voltage Law -

    Kirchhoff's loop rule states that the sum of all EMFs and voltage drops around any closed circuit loop equals zero, a foundational EMF voltage concept. This principle lets you solve complex circuits by balancing sources and resistive drops. In quizzes, set ∑ε - ∑IR = 0 to systematically find unknown voltages.

  5. Measuring EMF with a Potentiometer -

    A potentiometer measures an unknown EMF by comparing it with a known reference without drawing current, making it a precise tool for define electromotive force experiments. You adjust the slider until the galvanometer reads zero, indicating matched potential differences. This method appears in electricity quiz questions as the gold standard for open-circuit readings.

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