Physics: Current Electricity Principles

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Questions and Answers

How does the resistance of a good conductor change with temperature?

It increases significantly. (correct)

It remains constant.

It becomes negative.

It decreases slightly.

Which material has a temperature coefficient of electrical resistance nearly zero?

Aluminum

Copper

Silver

Constantan (correct)

What happens when the positions of the galvanometer and battery in a Wheatstone's bridge are interchanged?

The bridge becomes unbalanced. (correct)

The bridge remains balanced.

The voltage drops.

The current increases.

What is the terminal potential difference of a cell when it is short-circuited?

Zero volts. Signup and view all the answers

How can 12 coulombs per minute be expressed in amperes?

2A Signup and view all the answers

What happens to the current density in a wire of non-uniform cross section carrying a steady current?

Neither current nor current density is constant Signup and view all the answers

If four resistors of one ohm each are connected to form a square, what is the resistance across one side of the square?

0.5Ω Signup and view all the answers

In a circuit where the cross-sectional areas at two points are in the ratio 1:2 and the current is 0.5A, what is the ratio of electrons flowing through the sections per second?

1:2 Signup and view all the answers

Which of the following statements accurately describes the drift speed of an electron in a conductor?

It is directly proportional to the area of cross-section Signup and view all the answers

What is the effective emf when three cells of emf 2V, 5V, and 7V are connected in parallel?

7V Signup and view all the answers

What happens to the resistivity of each piece when a wire of resistance R is cut in half?

It becomes unchanged Signup and view all the answers

If a cell of emf E is connected across a conductor with resistance R, what is the expression for the internal resistance of the cell if the potential difference observed is V?

R(E-V) Signup and view all the answers

What mathematical relation describes the relationship between electric current and current density in a conductor?

I = J × A Signup and view all the answers

What is the resistance between any two terminals when three resistances of 5Ω are connected in a triangular form?

2.5Ω Signup and view all the answers

What is the formula for calculating the resistivity ρ of a material, given the potential difference V, current density J, length l, and area A?

$\frac{Vl}{J}$ Signup and view all the answers

How does the drift speed of electrons relate to the current, charge density, and area of cross-section in a conductor?

Drift speed is proportional to current and inversely proportional to charge density. Signup and view all the answers

When connected for maximum current, how should five cells each with an emf of 1.5V and an internal resistance of 0.1Ω be arranged in a circuit with an external resistor of 10Ω?

Cells in parallel. Signup and view all the answers

What is the physical meaning of mobility in the context of charge carriers in a conductor?

Mobility refers to the velocity of charge carriers under an electric field. Signup and view all the answers

What can be inferred about a material if its resistivity decreases with increasing temperature?

The material is a conductor. Signup and view all the answers

What will happen to the drift velocity of electrons if the electric current in a conductor of uniform cross section is increased by 20%?

It increases by 20% Signup and view all the answers

What is the required configuration of three resistors R₁ = 1Ω, R₂ = 2Ω, and R₃ = 2Ω to achieve an equivalent resistance of 2Ω?

Connect R₂ and R₃ in series, then in parallel with R₁ Signup and view all the answers

What is the equivalent resistance between points P and Q if each resistor in the circuit is of 10 Ω?

10 Ω Signup and view all the answers

If the electric current is decreased by 20%, what will be the effect on the drift velocity of electrons?

It will decrease Signup and view all the answers

In a circuit with three resistors connected in parallel, how does the equivalent resistance compare to the individual resistances?

It is less than the smallest resistor Signup and view all the answers

What is the internal resistance of a cell if the potential difference drops from 4V to 2V when a current of 2A is drawn?

2Ω Signup and view all the answers

How is the heat produced in wires related to their specific resistance when the potential difference is constant?

Heat produced is directly proportional to the specific resistance. Signup and view all the answers

What is drift velocity in the context of electricity?

The average speed of electrons in a conductor. Signup and view all the answers

What is the formula for calculating the resistance of a metal with a specific resistance and a known length?

$R = \rho \times L$ Signup and view all the answers

In a balanced Wheatstone's bridge, what is the condition of the currents?

No current flows through the galvanometer. Signup and view all the answers

What is the dimension of resistance?

ML^2T^{-3}I^{-2} Signup and view all the answers

Which relationship defines Ohm’s Law?

V = IR Signup and view all the answers

How does the resistance of a material relate to its temperature?

Resistance increases with temperature. Signup and view all the answers

To achieve maximum current in a circuit, what should be the relationship between the external resistor and the internal resistance of the battery?

R = r Signup and view all the answers

What is the formula for calculating current if the current density (J) is known?

I = J/A Signup and view all the answers

How is mobility of charge carriers defined?

Rate of charge flow per electric field. Signup and view all the answers

What will happen to the drift speed of electrons when the potential difference across a conductor is increased?

Drift speed will increase. Signup and view all the answers

For a circuit with 5 cells of 1.5V each connected in series, what is the total electromotive force (emf)?

7.5V Signup and view all the answers

What is the formula to calculate current if the conductivity (σ) and voltage (V) are known?

I = V/σ Signup and view all the answers

If the length ratio of a copper wire to an aluminum wire is 1:2, and their resistivity ratio is 5:9, how do their resistances compare?

Copper has lower resistance. Signup and view all the answers

What is the equivalent capacitance between points A and B?

1 µF Signup and view all the answers

How will the capacitance change if a very thin metal plate is placed at the middle of the two plates of the capacitor?

It will remain unchanged if the plate is very small. Signup and view all the answers

What is the charge on each capacitor when connected in series?

1200 µC Signup and view all the answers

What is the net potential difference across all capacitors connected in series?

550 V Signup and view all the answers

What is the effective capacitance (Cp) of the capacitors connected in parallel?

24 µF Signup and view all the answers

What is the potential difference across each capacitor when connected in parallel?

150 volts for all Signup and view all the answers

How is the total charge calculated when capacitors are connected in parallel?

Q = Q1 + Q2 + Q3 Signup and view all the answers

If n small identical charged liquid drops coalesce to form a large drop, what can be inferred about the potential of the large drop?

It will depend on the number of small drops. Signup and view all the answers

What is the capacity of the earth considered as a conducting sphere of radius 6.5 x 10^3 km?

722.2 µF Signup and view all the answers

What is the formula for calculating the capacity of a sphere?

$C = 4πεR$ Signup and view all the answers

If a sphere has a radius of 90 cm and can be charged to a potential of 1000 volts, which value represents its charge?

80 µC Signup and view all the answers

What unit represents the capacity for a spherical conductor found in the calculations?

Capacitance in farads Signup and view all the answers

In the formula $C = 4πεR$, what does the symbol 'ε' represent?

Permittivity of free space Signup and view all the answers

What is the formula for calculating the dielectric constant (K)?

$K = rac{E_1}{E_1 - E_2}$ Signup and view all the answers

If the initial electric field intensity $E_1$ is 100 and the intensity decreases to 80 after inserting a dielectric, what is the dielectric constant?

5 Signup and view all the answers

In a parallel grouping of capacitors, how is the total capacitance calculated?

$C_p = C_1 + C_2 + C_3 + C_4$ Signup and view all the answers

What is the equivalent capacitance of two capacitors of 1.5 µF each connected in parallel?

3 µF Signup and view all the answers

In the given scenario of capacitors, if two 3 µF capacitors are in series with the parallel combination, what determines the overall capacitance?

The lowest individual capacitance in series Signup and view all the answers

Study Notes

Current Electricity Basics

Resistance of good conductors decreases with temperature increase; some materials have negligible temperature coefficients.
The relationship between resistance and dimensions is crucial: for two wires of the same material, if one wire is longer and thicker, its resistance can be calculated using the geometric proportions.
Internal resistance exists in cells, affecting the terminal potential difference when a load is applied.

Circuit Laws and Applications

Kirchhoff's Laws help analyze current and voltage in electrical circuits: the junction rule (current at a junction) and loop rule (voltage around a closed loop).
A Wheatstone bridge remains balanced when the ratio of resistances is equal; swapping battery and galvanometer does not disrupt equilibrium.

Drift Velocity and Current Density

Drift velocity of electrons in a conductor is typically very slow (in mm/s), while current density relates directly to applied voltage and cross-sectional area.
Mobility of charge carriers indicates how quickly they can move through a conductor under an electric field.

Resistivity and Conductance

Resistivity depends on the material and affects how resistances are measured; temperature changes can alter resistivity.
Conductance is the reciprocal of resistance, highlighting easier current flow through certain materials.

Series and Parallel Circuits

In series circuits, total resistance increases, while in parallel, the effective resistance decreases.
Kirchhoff's laws can be applied to deduce the effective resistance and current in complex configurations.

Thermal Effects in Circuits

Heat produced in wires is related to specific resistance; hotter wires have increased resistance affecting overall circuit performance.
Larger currents through a conductor can raise the temperature, altering the properties of materials used.

Electromotive Force (EMF)

EMF is the energy provided by a cell per unit charge; potential difference indicates voltage drop due to internal resistance under load.
The performance of a cell in a circuit can be maximized by matching external resistance to internal resistance.

Direct Current (DC) Fundamentals

Current through resistors is determined by Ohm’s law, indicating the relationship between voltage, current, and resistance.
Resistance calculations for multiple components, especially with non-uniform materials or geometries, require careful consideration of geometrical factors.

Practical Applications

Circuit diagrams are essential for visualizing electrical paths and components for proper connection and analysis under various configurations.
Understanding how current behaves in diverse materials and setups aids in efficient electrical design and troubleshooting practices.

Charge and Current Calculations

The relationship between charge, current, and time allows calculations of total charge transfer over given intervals based on varying current conditions.
Drift velocity and area of cross-section play significant roles in defining the movement of electrons in circuit contexts.

Additional Concepts

The behavior of different resistors in various temperature and material states highlights the importance of understanding physical properties in electrical applications.
Capacitors also play significant roles in electrical circuits, storing energy and affecting current flow, especially in oscillatory circuits.

Yearly Specific Questions and Concepts

Questions from various years emphasize the practical understanding and application of resistance, voltage, current, capacitance, and the instructions related to circuit design and analysis.
Problem-solving in electrical circuits fosters a deep understanding of theoretical and practical aspects necessary for mastering current electricity concepts.

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Description

Test your understanding of the fundamentals of current electricity with this quiz. Explore concepts such as resistance, Kirchhoff's laws, and drift velocity. This quiz covers essential principles and applications that govern electrical circuits.