Current Electricity MCQs | Physics MCQs

A longer wire leads to a smaller potential gradient (potential drop per unit length), meaning a small voltage corresponds to a larger, more measurable length.

Despite the electric signal traveling near the speed of light, the net forward motion of individual electrons is very slow due to constant collisions.

For parallel resistors, 1/Req = 1/R₁ + 1/R₂ + 1/R₃ = 1/2 + 1/3 + 1/6 = (3+2+1)/6 = 1. Therefore, Req = 1 Ω.

Red=2, Violet=7, Brown multiplier=10¹, Gold tolerance=5%. This gives 27 × 10¹ = 270 Ω with 5% tolerance.

When length (L) is doubled, the cross-sectional area (A) is halved (volume is constant). Since R ∝ L/A, the new resistance R' ∝ (2L)/(A/2) = 4(L/A) = 4R.

A semiconductor diode has a non-linear V-I graph, meaning its resistance is not constant and it does not obey Ohm's law.

For semiconductors, an increase in temperature frees more charge carriers, which increases conductivity and therefore decreases resistance.

Power P = I²R = (2)² × 5 = 20 W. Energy E = Power × time = 20 W × 10 s = 200 J.

This is the maximum power transfer theorem, which states that maximum power is delivered to the load when the load resistance equals the source's internal resistance.

The 60W bulb has higher resistance (R=V²/P). In series, current is the same, so the bulb with higher resistance dissipates more power (P=I²R) and glows brighter.

A rheostat is a three-terminal variable resistor used to control the amount of current flowing in a circuit.

Using the shunt formula S = (Ig * G) / (I - Ig). Here, G=95 Ω, Ig = 5 mA = 0.005 A, and I = 5 A. So, S = (0.005 * 95) / (5 - 0.005) = 0.475 / 4.995 ≈ 0.095 Ω.

This is the statement of Kirchhoff's Voltage Law (Loop Rule), which is based on the conservation of energy.

A meter bridge is a practical implementation of the Wheatstone bridge used to find an unknown resistance by achieving a balanced condition.

In electrolytic solutions, the current is carried by the movement of both positive ions (cations) and negative ions (anions).

An ammeter is connected in series, so it must have negligible resistance to avoid altering the current it is intended to measure.

Resistance of 25W bulb, R₁ = V²/P = 220²/25 = 1936 Ω. Resistance of 100W bulb, R₂ = 220²/100 = 484 Ω. In series, current I = 440 / (1936+484) = 0.18 A. Voltage across 25W bulb = IR₁ = 0.18 * 1936 ≈ 348 V. Since 348 V is much greater than its rated voltage of 220 V, the 25 W bulb will fuse.

A voltmeter is connected in parallel, so it must have very high resistance to avoid drawing current from the main circuit and altering the potential difference.

Current I = Q/t. The total time t = 1 minute + 30 seconds = 60 s + 30 s = 90 s. So, I = 90 C / 90 s = 1.0 A.

Specific resistance (resistivity) is an intrinsic property of a material that is dependent on its atomic structure and temperature.

Drift velocity is directly proportional to the electric field (E), and E is directly proportional to the potential difference (V). Therefore, doubling V doubles the drift velocity.

A fuse needs high resistance to heat up effectively (P=I²R) with excess current, and a low melting point to break the circuit before damage occurs.

Increasing the temperature of a semiconductor provides energy to release more charge carriers (electrons and holes), thus increasing its conductivity and decreasing its resistance.

Total resistance R_total = R_ext + r = 4Ω + 1Ω = 5Ω. Current I = E / R_total = 10V / 5Ω = 2A.

Terminal potential difference Vt = E - Ir = 10V - (2A)(1Ω) = 8V. Alternatively, it's the voltage across the external resistor: Vt = I * R_ext = 2A * 4Ω = 8V.

Alloys like Manganin are used because they have high resistivity and a very low temperature coefficient of resistance, ensuring a stable potential gradient.

Original resistance R = ρ(L/A). New resistance R' = ρ((L/2)/(2A)) = (1/4) * ρ(L/A) = R/4.

From Ohm's law V = IR, if V is on the y-axis and I is on the x-axis, the slope (ΔV/ΔI) is equal to the resistance R.

Current I = Q/t = (ne)/t. Q = 10⁷ × (1.6 × 10⁻¹⁹ C) = 1.6 × 10⁻¹² C. Since t=1s, the current is 1.6 × 10⁻¹² A.

Between any two vertices, two resistors are in series (3+3=6Ω), and this combination is in parallel with the third resistor (3Ω). 1/Req = 1/6 + 1/3 = 3/6 = 1/2. So, Req = 2Ω.

Joule's law of heating states that the heat produced in a resistor is proportional to the square of the current, the resistance, and the time (H = I²Rt).

Yellow=4, Violet=7, Red multiplier=10². This gives 47 × 10² = 4700 Ω = 4.7 kΩ.

A low-resistance shunt is connected in parallel to divert most of the current, allowing the sensitive galvanometer to measure a small fraction of the total current.

A high resistance (multiplier) is connected in series to limit the current and allow the galvanometer to measure a large potential difference across the combination.

A potential divider uses series resistors to provide a fraction of the input voltage as an output, which can be fixed or variable.

The series combination gives R_series = 10 Ω + 30 Ω = 40 Ω. This is in parallel with 20 Ω. The equivalent resistance Req is 1/Req = 1/40 + 1/20 = (1+2)/40 = 3/40. So, Req = 40/3 ≈ 13.33 Ω.

Conductivity is the reciprocal of resistivity (Ω-m). Its unit is 1/(Ω-m), which is also called Siemens per meter (S/m).

In the absence of an external electric field, the random velocities of electrons are in all directions and cancel each other out, resulting in no net flow of charge.

Current I = Q/t. Time must be in seconds: 5 minutes = 300 s. So, I = 600 C / 300 s = 2 A.

The temperature at which a material's resistance abruptly drops to zero is known as its critical temperature (Tc).

Adding resistors in parallel provides more paths for the current, which reduces the overall opposition to flow. Thus, the total resistance is always less than the smallest individual resistor.

Using the power formula P = VI, the current I = P / V = 100 W / 200 V = 0.5 A.

The materials inside a cell, such as its electrolyte and electrodes, offer some opposition to the flow of charge, and this is called the internal resistance.

By finding the balancing lengths for two different cells, a potentiometer can be used to accurately determine the ratio of their EMFs (E₁/E₂ = L₁/L₂).

Insulators have extremely high resistivity, typically ranging from 10¹⁰ to 10¹⁶ Ω-m, because they have very few free charge carriers.

Power is given by P = I²R. If the current (I) is doubled to 2I, the new power P' = (2I)²R = 4I²R, which is four times the original power.

Potential gradient (k) is defined as the fall of potential per unit length of the potentiometer wire, k = V/L.

Sensitivity is maximized when all four resistances (R₁, R₂, R₃, R₄) are comparable. This ensures that a small imbalance causes a detectable current in the galvanometer.

The Junction Rule is based on the conservation of charge, a fundamental principle that applies to any circuit, whether AC or DC.

The fourth band on a resistor indicates tolerance. Gold represents ±5% tolerance, and silver represents ±10% tolerance.

For identical cells in parallel, the equivalent EMF remains the same (E), while the equivalent internal resistance is calculated like parallel resistors (1/r_eq = 1/r + 1/r), resulting in r/2.

Despite its name, EMF is not a force. It is energy per unit charge, just like potential difference, and is measured in Volts (V).

During charging, the external power source must overcome the battery's own EMF and the internal voltage drop. Thus, the terminal voltage is higher than the EMF.

NTC stands for 'Negative Temperature Coefficient'. This means its resistance has an inverse relationship with temperature; as temperature goes up, resistance goes down.

Energy is power multiplied by time (E = P × t). Since power can be expressed as P = VI, the energy dissipated is E = VIt.

A voltmeter has a very high internal resistance. Placing it in series adds this large resistance to the circuit, drastically increasing the total resistance and reducing the current to a negligible amount.

Energy consumed (in kWh) = Power (in kW) × time (in hours) = 2 kW × 5 h = 10 kWh. Total cost = Energy consumed × cost per unit = 10 kWh × Rs. 9/kWh = Rs. 90.

Parallel connection ensures that all appliances are connected across the same two points of the main supply, thus receiving the same, full line voltage (e.g., 220V).

This equation, J = σE, is the microscopic or point form of Ohm's Law, relating the current density at a point to the electric field at that point.

From the definition of current (I = Q/t), charge (Q) is equal to current multiplied by time (I × t). Therefore, 1 Coulomb = 1 Ampere × 1 second.

An electric fuse contains a wire with a low melting point that heats up and melts (breaks the circuit) when the current exceeds a safe level, based on Joule's law of heating.

Semiconductors like silicon and germanium have electrical properties intermediate to those of good conductors and good insulators.

The slope is ΔI/ΔV. Since resistance R = V/I, the slope is 1/R, which is defined as conductance (G).

Devices like semiconductor diodes, transistors, and vacuum tubes are non-ohmic because their current-voltage relationship is not linear.

Using the formula E = I(R + r). We have 6 = 1.0(R + 0.5). So, 6 = R + 0.5, which gives R = 5.5 Ω.

The maximum potential drop that can be measured by the potentiometer is the EMF of its driver cell. Therefore, the driver EMF must be greater than the unknown EMF to find a balance point.

The low-resistance shunt bypasses or 'shunts' the majority of the current around the sensitive galvanometer, allowing the instrument to measure a much larger total current.

From the equation I = nAv_d, if current (I) is constant and area (A) decreases, the drift velocity (v_d) must increase to maintain the equality.

Using the power formula P = V²/R, we can solve for resistance: R = V²/P = (6V)² / 12W = 36/12 = 3 Ω.

The meter bridge follows the Wheatstone principle: R₁/R₂ = L₁/L₂. So, 6/R_unknown = 40/(100-40) = 40/60. R_unknown = 6 × (60/40) = 9 Ω.

Relaxation time is the average time between collisions. Lowering the temperature reduces the thermal vibrations of the metal lattice, leading to fewer collisions and thus a longer average time between them.

Using E = I(R + r), we have 1.5 = 2(0.5 + r). So, 0.75 = 0.5 + r, which gives the internal resistance r = 0.25 Ω.

Using R_T = R₀(1 + αΔT), where ΔT = T_final - T_initial. 20 = 5(1 + 0.004(T - 20)). This simplifies to 4 = 1 + 0.004(T - 20), so 3 = 0.004(T-20). T-20 = 3/0.004 = 750. Therefore, T = 750 + 20 = 770°C.

A resistor is a passive component that only dissipates electrical energy as heat. Sources of EMF (like cells, generators) convert other forms of energy into electrical energy.

Current is charge/time (A = C/s). Therefore, charge = current × time. Ampere-hour is a unit of current multiplied by time, making it a unit of electric charge, commonly used for battery capacity.