intro
Question 1:
What will be the equivalent resistance of the combination when a wire with resistance R is cut into N equal parts, and these parts are then connected in parallel?
Topic: Resistance in Parallel Circuits
Correct Answer: C) R/N2
- When a wire of resistance R is cut into N equal parts and connected in parallel, each part will have a resistance of NR.
- In a parallel circuit, the total or equivalent resistance (Req) is given by the formula 1/Req = Sum(1/Ri), where Ri is the resistance of each part.
- Substituting NR for each Ri, we get 1/Req = N/(NR) which simplifies to 1/Req = 1/(NR). Solving for Req gives Req = R/N2.
Question 2:
What is the equivalent resistance when three resistors with resistances of 500 ohms, 350 ohms, and 500 ohms are connected in series?
Topic: Resistance in Series Circuits
Correct Answer: B) 1350 Ω
- In a series circuit, the equivalent resistance (Re) is simply the sum of the individual resistances.
- Therefore, Re = R1 + R2 + R3 = 500 + 350 + 500 = 1350 ohms.
- Hence, the correct answer is B, "1350 Ω".
Question 3:
If the resistance of a 60W bulb for use in Pakistan with 220V is R, what would be the resistance of a similar 60W bulb for use in USA with 110V?
Topic: Resistance and Voltage
Correct Answer: C) R/4
- The power P of an electrical device is given by the formula P = V2/R, where V is the voltage and R is the resistance.
- If two bulbs have the same power but are used with different voltages, the resistance will be different.
- Therefore, if P1 = P2, then V12/R1 = V22/R2. Rearranging to solve for R2 gives R2 = (V22/V12) * R1.
- Substituting the given values gives R2 = (1102/2202) * R = R/4.
Question 4:
If E is the EMF of a battery, what will be the voltage drop across the terminals when an external resistance R equals the internal resistance r?
Topic: EMF and Voltage Drop
Correct Answer: A) E/2
- The total voltage E of a battery is distributed as a potential drop (V) across the internal resistance r and the external resistance R.
- If r equals R, the equation becomes E = 2IR.
- Solving for V (the voltage drop across the external resistance) gives V = E/2.
Question 5:
What is true about the total resistance (R) when two resistors with resistances R1 and R2 are connected in parallel?
Topic: Resistance in Parallel Circuits
Correct Answer: D) R < minimum of R1 and R2
- In a parallel circuit, the total resistance is found by the formula 1/R = 1/R1 + 1/R2.
- Given this, it is apparent that the total resistance in a parallel circuit is always less than the smallest individual resistance.
- Hence, the correct answer is D, "R < minimum of R1 and R2".
Question 6:
What causes the flow of current in metals?
Topic: Electric Current
Correct Answer: C) Electrons
- Charged particles flow through electric current. In metals, these particles are the free electrons.
- Protons are bound within the atomic nucleus, and neutrons do not carry a charge.
- Thus, in metals, the flow of current is due to the movement of electrons.
- Hence, the correct answer is C, "Electrons".
MCQs 7:
What is the resistance of an open circuit?
Topic: Circuit Resistance
Correct Answer: A) Infinite
- In an open circuit, there is a break in the path that prevents current from flowing.
- Using Ohm's law, we can express resistance as R = V/I.
- In an open circuit, the current (I) is zero.
- Therefore, the resistance in an open circuit is V/0, which is infinite.
- Hence, the correct answer is A, "Infinite".
MCQs 8:
Considering three resistors R1, R2, and R3, that are linked in a sequential manner. Assuming that R1 > R2 > R3, what can be said about the composite resistance?
Topic: Resistor Series Connection
Correct Answer: D) More than R1
- When resistors are combined in a series, the total resistance is computed as the sum of the individual resistances.
- Therefore, the equivalent resistance in a series connection is greater than any of the individual resistances.
- Hence, the correct answer is D, "More than R1".
Question 9:
What is the purpose of having a fuse connected in sequence with the circuit?
Topic: Circuit Protection
Correct Answer: B) To protect from high current
- When a circuit's current exceeds a specified level, a fuse interrupts the flow of electricity.
- Circuits are protected from high currents and short circuits by fuses.
- Therefore, the correct answer is B, "To protect from high current".
Question 10:
Given that the current in the 3Ω resistor is 4A, what would be the potential difference between points labelled as "A" and "B" in the given circuit diagram?
Topic: Potential Difference
Correct Answer: D) 20 V
- The potential difference or voltage V across a resistor can be calculated using the formula V = IR, where I denotes current and R is the resistance.
- In this case, the total resistance between points A and B is the sum of the individual resistances (3Ω + 2Ω = 5Ω).
- Substituting the given values into the formula, we get V = (4A)*(5Ω) = 20V.
- Therefore, the correct answer is D, "20 V".
Question 11:
What happens to the resistance when the size and diameter of a conductor are both increased two-fold?
Topic: Resistance and Conductor Dimensions
Correct Answer: B) It gets halved
- The resistance (R) of a conductor is given by the formula R = ρ(L/A), where ρ denotes resistivity, L denotes length, and A is the cross-sectional area of the conductor (proportional to the square of the diameter).
- If both the length and diameter of the conductor are doubled, the new area is four times the original, and hence, the new resistance will be half the original.
- Therefore, the correct answer is B, "It gets halved".
Question 12:
What is the equivalent of 1 kilowatt-hour in electronvolts (eV)?
Topic: Energy Conversion
Correct Answer: A) 2.25×1025 eV
- Physicists use electronvolts (eV) to measure energy, which is measured in kilowatt hours (kWh).
- 1 kWh is equivalent to approximately 2.25×1025 eV.
- Hence, the correct answer is A, "2.25×1025 eV".
Question 13:
What is the impact on the conductance of a wire if its length is extended to twice its original value?
Topic: Conductance and Wire Length
Correct Answer: B) Halved
- As G = 1/R, conductance (G) is the reciprocal of resistance (R).
- A doubled wire's length doubles its resistance (assuming all other factors remain constant), reducing its conductance by half.
- So, the correct answer is B, "Halved".
Question 14:
What does internal resistance refer to?
Topic: Internal Resistance
Correct Answer: D) Resistance due to an electrolyte
- Internal resistance is the inherent resistance within a power source or electronic device, caused by the materials within it.
- In a cell, for instance, the electrolyte between the two electrodes contributes to the internal resistance.
- Therefore, the correct answer is D, "Resistance due to an electrolyte".
Question 15:
When is the power supplied by an internal resistor to an external load, denoted 'R', at its maximum?
Topic: Power Delivery
Correct Answer: A) When internal resistance 'r' equals 'R'
- The power 'P' delivered to an external load is at its maximum when the internal resistance 'r' is equal to the external resistance 'R'.
- This is because the denominator of the power expression is minimized, thereby maximizing 'P'.
- Hence, the correct answer is A, "When internal resistance 'r' equals 'R'".
Question 16:
If a light bulb rated at 100 watts is connected to a 220V supply, what would be the resistance of the bulb's filament?
Topic: Resistance Calculation
Correct Answer: B) 484 ohms
- The resistance 'R' of a device can be calculated using the formula R = V^2/P, where 'V' is the voltage and 'P' is the power.
- Substituting the given values into the formula, we get R = (220V)^2 / 100W = 484 ohms.
- So, the correct answer is B, "484 ohms".
Question 17:
If you have 500 ohm resistors at your disposal, how would you arrange these to obtain a total resistance of 750 ohms?
Topic: Resistance Combination
Correct Answer: D) Align two 500-ohm resistors in parallel and combine this with another 500-ohm resistor in series
- The total resistance of several resistors in series is the sum of their resistances.
- Parallel resistors, on the other hand, sum the reciprocals of their individual resistances to determine their total resistance.
- Therefore, to achieve 750 ohms from 500-ohm resistors, you should arrange two in parallel (forming 250 ohms) and then connect this with another 500-ohm resistor in series (adding 500 ohms) to form 750 ohms.
- Hence, the correct answer is D, "Align two 500-ohm resistors in parallel and combine this with another 500-ohm resistor in series".
Question 18:
Consider a wire with resistance 'R' that is divided into four equal segments and then connected in parallel. What would the equivalent resistance be?
Topic: Resistance of Wire Segments
Correct Answer: C) R/16
- When a wire is divided into equal segments, the resistance of each segment is proportional to its length. Therefore, each segment has a resistance of R/4.
- When these segments are connected in parallel, the total resistance is given by the reciprocal of the sum of their reciprocals, which in this case is R/16.
- Hence, the correct answer is C, "R/16".
Question 19:
Identify the correct formula for calculating electric current:
Topic: Current Calculation
Correct Answer: B) I = qf
- A current (I) is a measure of the speed at which an electric charge (q) flows, and can be expressed as I = q/t, where t is time.
- If we express time in terms of frequency (f) where f = 1/t, we get I = qf as the formula for electric current.
- Therefore, the correct answer is B, "I = qf".
Question 20:
What is the standard unit for Electromotive Force (EMF)?
Topic: Measurement of Electromotive Force
Correct Answer: C) Volt
- Electromotive force (EMF) is measured in volts.
- Specifically, EMF is the energy change experienced by a unit charge as it travels around a circuit, which is represented as E = Δw/Δq.
- The unit of energy is Joule (J), and the unit of charge is Coulomb (C). Therefore, the unit of EMF is J/C, which is equal to a Volt (V).
- Thus, the correct answer is C, "Volt".
MCQs 21:
If a conducting wire is elongated to triple its original length, how would this impact its resistance?
Topic: Impact of Length on Resistance
Correct Answer: C) The resistance increases nine-fold
- There is a direct relationship between wire resistance and length, according to the formula R = ρL/A, where R is resistance, ρ is resistivity, L is length, and A is cross-sectional area.
- If the length of the wire is tripled (while keeping the cross-sectional area constant), the resistance will become nine times the original, as the increase in resistance is proportional to the square of the length.
MCQs 22:
What is the maximal power delivered to a load resistance?
Topic: Maximum Power Transfer
Correct Answer: A) E2/4R
- In the case in which the load's resistance equals the source's internal resistance, the Maximum Power Transfer Theorem states that the source transfers the most power to the load.
- The power 'P' delivered to a load 'R' is given by the formula P = E2/4R, where E is the electromotive force (EMF).
Question 23:
In relation to an open circuit, which of the following statements is true?
Topic: Electric Potential in Open Circuits
Correct Answer: A) E equals Vt
- In an electrical circuit, the electromotive force (E) is expressed as E = Vt + Ir, where Vt is terminal voltage and Ir is the current (I) times the load resistance (r).
- For an open circuit, the current flow is zero (I = 0).
- Substituting I = 0 in the above equation gives E = Vt.
Question 24:
Siemen is a unit of measurement for:
Topic: Units of Electrical Measurements
Correct Answer: C) Conductance
- In electrical terminology, 'Siemen' is the SI unit used for measuring conductance.
- Conductance is the reciprocal of resistance, i.e., Conductance = 1/Resistance.
- Therefore, the unit of conductance is the reciprocal of the unit of resistance (Ohm), which is Siemen (Ω^-1).
Question 23:
In relation to an open circuit, which of the following statements is true?
Topic: Electric Potential in Open Circuits
Correct Answer: A) E equals Vt
- In an electrical circuit, the electromotive force (E) is expressed as E = Vt + Ir, where Vt is terminal voltage and Ir is the current (I) times the load resistance (r).
- For an open circuit, the current flow is zero (I = 0).
- Substituting I = 0 in the above equation gives E = Vt.
- Thus, the correct answer is A, "E equals Vt".
Question 24:
Siemen is a unit of measurement for:
Topic: Units of Electrical Measurements
Correct Answer: C) Conductance
- In electrical terminology, 'Siemen' is the SI unit used for measuring conductance.
- Conductance is the reciprocal of resistance, i.e., Conductance = 1/Resistance.
- Therefore, the unit of conductance is the reciprocal of the unit of resistance (Ohm), which is Siemen (Ω^-1).
- Consequently, the correct answer is C, "Conductance".
Question 25:
In the context of a metallic wire, how does the ratio of voltage to the corresponding current react with a rise in temperature?
Topic: Ohm's Law and Temperature Effects
Correct Answer: B) It increases with a rise in temperature
- According to Ohm's law, the ratio of voltage (V) to current (I) is equal to the resistance (R) of the wire (V/I = R).
- The resistance of a metallic wire increases as the temperature rises, given the properties of most metals.
- Thus, as per Ohm's law, with an increase in resistance (owing to the rise in temperature), the ratio of voltage to the corresponding current also increases.
Question 26:
What will be the equivalent resistance if a resistor of resistance R is divided into three equal parts and then connected in parallel?
Topic: Resistor Calculations in Parallel Circuits
Correct Answer: C) R/9
- When a resistor of resistance 'R' is cut into three equal parts, the resistance of each part becomes R/3.
- If these parts are connected in parallel, the equivalent resistance (Re) would be calculated using the formula 1/Re = 1/R1 + 1/R2 + 1/R3. In this case, R1, R2, and R3 are all R/3.
- Substituting these values into the formula would give us 1/Re = 3/(R/3), simplifying which would yield Re = R/9.
Question 27:
Which of the following is not capable of generating an electric current?
Topic: Sources of Electric Current
Correct Answer: C) Electric Iron
- An electric generator, a thermocouple, and a solar cell are all devices that can generate an electric current.
- An electric generator does so by converting mechanical energy into electrical energy.
- A thermocouple generates electricity by taking advantage of the Seebeck effect, where a voltage is created in the presence of a temperature differential between two different metals or semiconductors.
- Electricity is generated by solar cells by converting solar energy.
- An electric iron, however, is a device that utilizes electric current to function and does not generate it.