Recent questions and answers in Physics

Given n resistors each of resistance R, how will you combine them to get the (i) maximum (ii) minimum effective resistance? What is the ratio of the maximum to minimum resistance?
Answer : The two fundamental ways to combine resistors are in **series** and in **parallel**. These two configurations yield the maximum and minimum possible resistances, respectively. --- ### (i) Maximum Effective Resistance To obtain the * ... {min} = R/n$ | | **Ratio** | $R_{max} / R_{min}$ | $n^2$ |...

A high tension (HT) supply of, say, 6 kV must have a very large internal resistance. Why?
Answer : The primary reason is **safety and current limiting**. Let's use Ohm's Law ($V = IR$) to understand this. A power supply can be modeled as an ideal voltage source ($V_s$) in series ... HT supply for **power transmission** has a very low internal resistance for **efficiency and power delivery**....

A low voltage supply from which one needs high currents must have very low internal resistance. Why?
Answer : ### The Simple Analogy: A Water Pipe Imagine your power supply is a large water tank (representing the voltage) and you need to get a high flow of water (high current) out of a pipe at ... extremely small, this will generate a massive amount of heat, which can damage or destroy the power supply....

Is ohm’s law universally applicable for all conducting elements? If not, give examples of elements which do not obey Ohm’s law.
Answer : The answer is no, **Ohm's law is not universally applicable for all conducting elements.** Ohm's law is an empirical rule, not a fundamental law of nature. It accurately describes the ... under stable conditions, but it is far from a universal law for all materials that conduct electricity....

A steady current flow in a metallic conductor of non-uniform crosssection. Which of these quantities is constant along the conductor: current, current density, electric field, drift speed?
Answer : Here is a detailed explanation for each quantity: ### 1. Current (I) * **Why it's constant:** The term "steady current" implies that the rate of flow of charge ($I = dQ/dt$) is constant. Due to the ... ($v_d$)** | Not Constant | $v_d = I/(nAe)$. Since A is not constant, $v_d$ is not constant. |...

Six lead-acid type of secondary cells each of emf 2.0 V and internal resistance 0.015 Ohm are joined in series to provide a supply to a resistance of 8.5 Ohm . What is the current drawn from the supply and its terminal voltage?
Answer : ### Given Data: * Number of cells, **n = 6** * EMF of each cell, **E_cell = 2.0 V** * Internal resistance of each cell, **r_cell = 0.015 Ω** * External resistance (load), **R = 8.5 Ω ... The current drawn from the supply is **1.40 A**. * The terminal voltage of the supply is **11.9 V**....

A storage battery of emf 8.0 V and internal resistance 0.5 Ohm is being charged by a 120 V DC supply using a series resistor of 15.5 Ohm . What is the terminal voltage of the battery during charging? What is the purpose of having a series resistor in the charging circuit?
Answer : ### Given Data: * Electromotive force (emf) of the battery, $E = 8.0 \text{ V}$ * Internal resistance of the battery, $r = 0.5 \text{ } \Omega$ * DC supply voltage, $V_{supply} = ... to a much safer and more manageable **7.0 A**, protecting both the battery and the power supply from damage....

A silver wire has a resistance of 2.1 Ohm at 27.5 degree C , and a resistance of 2.7 Ohm at 100 degree C . Determine the temperature coefficient of resistivity of silver.
Answer : ### 1. Understand the Principle The relationship between resistance and temperature for most metals (like silver) over a moderate temperature range is approximately linear and can be described by the formula: $R_2 = ... 00394 °C⁻¹** Alternatively, in scientific notation: **α = 3.94 x 10⁻³ °C⁻¹**...

Three resistors 1 Ohm , 2 Ohm and 3 Ohm are combined in series. What is the total resistance of the combination?
Answer : When resistors are combined in series, the total resistance is the sum of the individual resistances. The formula is: R_total = R1 + R2 + R3 Given the values: * R1 = 1 Ω * R2 = 2 Ω * R3 = 3 Ω ... = 1 Ω + 2 Ω + 3 Ω = 6 Ω So, the total resistance of the combination is **6 Ohms**....

A battery of emf 10 V and internal resistance 3 Ohm is connected to a resistor. If the current in the circuit is 0.5 A, what is the resistance of the resistor? What is the terminal voltage of the battery when the circuit is closed?
Answer : ### Given Information: * **EMF of the battery (E):** 10 V * **Internal resistance (r):** 3 Ω * **Current in the circuit (I):** 0.5 A --- ### 1. What is the resistance of the ... text{V}$ Both methods give the same result. **Answer:** The terminal voltage of the battery is **8.5 V**....

Define emf. of a cell? On what factors does it depend?
Answer : ### Definition of EMF (Electromotive Force) The **EMF (Electromotive Force)** of a cell is defined as the maximum potential difference between its two terminals when no current is being drawn ... *, not its EMF. A larger distance increases the path ions must travel, increasing internal resistance....

Three identical cells, each of emf. 2V and unknown internal resistance are connected in parallel. This combination is connected to a 5 ohm resistor. If the terminal voltage across the cell is 1.5 volt. What is the internal resistance of each cell? Hence define the internal resistance of a cell?
Answer : ### Part 1: Calculating the Internal Resistance Here's how we can find the internal resistance of each cell. **Given Data:** * Electromotive force (EMF) of each cell, E = 2 V * Number of identical cells ... . * **I** is the current flowing from the cell. * **r** is the internal resistance....

A cylindrical wire is stretched to increase its length by 10% calculate the percentage increase in resistance?
Answer : The percentage increase in resistance is **21%**. Here is the step-by-step calculation and explanation: ### The Key Concepts 1. **Resistance Formula:** The resistance (R) of a wire is given by: $R = \ ... R_1}{R_1} \times 100\%$ $\text{Percentage Increase} = 0.21 \times 100\% = \bf{21\%}$...

Obtain ohm’s law from the expression for electrical conductivity.
Answer : We can derive the familiar form of Ohm's Law ($V=IR$) by starting with the fundamental expression for electrical conductivity ($\sigma$). This derivation beautifully connects the microscopic behavior of ... total **current ($I$)** flowing through it, successfully obtaining Ohm's Law, $V=IR$....

Find the value of unknown resistance X in the circuit shown in the figure if no current flows through the section AO. Also calculate the current drawn by the circuit from the battery of emf. 6V ... resistance. ![][1] [1]: https://electrical-engineering.app/?qa=blob&qa_blobid=394010198424626099
Answer : ### Part 1: Finding the value of the unknown resistance X The problem states that no current flows through the section AO. Let's label the central junction point as 'O'. 1. **Identify the Principle:** The ... resistance **X is 6Ω**. * The current drawn by the circuit from the battery is **1A**....

A battery of emf E and internal resistance r sends a current, I1 , I2 when connected to an external resistance of R1 , R2 respectively. Find the emf. and internal resistance of the battery.
Answer : Let's derive the expressions for the electromotive force (EMF) and the internal resistance of the battery step-by-step. ### Understanding the Setup The core principle we'll use is Ohm's law applied to the entire circuit. For a ... $$ **EMF (E):** $$ E = \frac{I_1 I_2 (R_1 - R_2)}{I_2 - I_1} $$...

State why the resistance of the conductor increases with the rise in temperature.
Answer : Here is a clear explanation of why the resistance of a conductor increases with a rise in temperature, broken down into a simple analogy and the underlying physics. --- ### Simple Analogy: The ... More collisions** mean more opposition to the flow, which is, by definition, **higher resistance**....

State and explain Kirchhoff’s law?
Answer : Kirchhoff's laws are two fundamental principles used to analyze electric circuits. They were formulated by Gustav Kirchhoff in 1845 and are based on the conservation of charge ... =blob&qa_blobid=16131873694589351449 [2]: https://electrical-engineering.app/?qa=blob&qa_blobid=10917265924274549047...

Explain with the help of a circuit diagram, how the value of an unknown resistance can be determined using a Wheatstone bridge?
Answer : ![][1] [1]: https://electrical-engineering.app/?qa=blob&qa_blobid=407323477172242274 ### **Introduction** A Wheatstone bridge is an electrical circuit used for the precise measurement of an ... (R₃) at the balance point has been recorded, the unknown resistance Rₓ can be calculated precisely....

What is drift velocity? Derive expression for drift velocity of electrons in a good conductor in terms of relaxation time of electrons?
Answer : --- ### Part 1: What is Drift Velocity? In a metallic conductor (like a copper wire), the outer electrons of the atoms are not bound to individual atoms. They are free to move throughout the entire volume of ... field. * The magnitude of the drift velocity is given by: $v_d = \frac{e\tau}{m}E$....

With suitable circuit diagram, show how emfs of 2 cells can be compared using a potentiometer?
Answer : ![][1] [1]: https://electrical-engineering.app/?qa=blob&qa_blobid=16022041933233000659 ### **Principle of a Potentiometer** A potentiometer works on the principle that the potential drop ... -section. 4. The current in the primary circuit should be kept constant throughout the experiment....

Why do we prefer a potentiometer to measure the emf of a cell rather than a voltmeter?
Answer : The primary reason we prefer a potentiometer to measure the EMF of a cell is that **a potentiometer draws no current from the cell at the point of measurement.** A voltmeter, by its ... method ensures no current is drawn, thereby eliminating any error caused by the source's internal resistance....

What happens to the resistance of the wire when its length is increased to twice its original length?
Answer : This gets to the core of how resistance works. The short and direct answer is: **The resistance of the wire will double.** Here's a more detailed explanation of why. ### 1. The Simple Explanation (Analogy) Think of the wire ... (x2) | Halves (x0.5) | **Quadruples (x4)** |...

In a potentiometer arrangement, a cell of emf 1.25V gives a balance point at 35.0cm length of the wire. If the cell is replaced by another cell and the balance point shifts to 63.0cm , what is the emf of the second cell?
Answer : ### Principle The working principle of a potentiometer is that the potential drop across any portion of a wire of uniform cross-section is directly proportional to the length of that portion, provided a constant current flows ... 2.25 V** ### Answer The EMF of the second cell is **2.25 V**....

The storage battery of a car has an emf of 12V . If the internal resistance of the battery is 0.4 Ohm , what is the maximum current that can be drawn from the battery?
Answer : The maximum current that can be drawn from the battery is **30 Amperes (A)**. --- ### Detailed Explanation #### 1. Understand the Concepts * **EMF (Electromotive Force, $\mathcal{E ... even explode. This calculation is a theoretical maximum. **Never attempt to short-circuit a car battery.**...

What are ohmic and non-ohmic resistors? Give one example of each?
Answer : **Ohm's Law** states that the voltage ($V$) across a conductor is directly proportional to the current ($I$) flowing through it, provided all physical conditions and temperature remain constant. Mathematically, ... | **Carbon Resistor**, Nichrome Wire | **Filament Light Bulb**, Diode, Thermistor |...

Why is constantan or manganin used for making standard resistors?
Answer : Constantan and manganin are used for making standard resistors for a specific combination of four key properties that make them ideal for precision applications. Here's a breakdown of why these alloys ... precision and stability required in a metrology lab, **manganin is the preferred material.**...

A set of n-identical resistors, each of resistance R ohm when connected in series have an effective resistance of X ohm and when the resistors are connected in parallel the effective resistance is Y ohm. Find the relation between R , X and Y ?
Answer : Let's break this down step-by-step to find the relationship between R, X, and Y. ### 1. Resistors in Series When resistors are connected in series, their total effective resistance is the sum of ... the **geometric mean** of the total series resistance (X) and the total parallel resistance (Y)....

Two heated wires of the same dimensions are first connected in series and then it’s parallel to a source of supply. What will be the ratio of heat produced in the two cases?
Answer : Here is the step-by-step solution: ### The Short Answer The ratio of heat produced in the series case to the parallel case is **1:4**. --- ### Detailed ... proportional to this current, the parallel circuit draws significantly more power and therefore produces significantly more heat....

A Carbon resistor has three strips of red colour and a gold strip. What is the value of the resistor? What is its tolerance?
Answer : The value of a carbon resistor is determined by the standard resistor color code system. For a 4-band resistor: * **Band 1:** First significant digit * **Band 2:** Second significant ... a new resistor with these color bands will have an actual resistance somewhere between 2090 Ω and 2310 Ω....

Two electric bulbs A and B are marked 220V , 40W and 220V 60W respectively. Which one has a higher resistance?
Answer : **The 40W bulb (Bulb A) has a higher resistance.** Here's the detailed explanation of why: ### The Relationship The relationship between Power (P), Voltage (V), and Resistance (R) is given by ... to get more water through a pipe; you need a wider pipe (less resistance) to increase the flow rate....

Two wires A and B are of the same metal and of same length have their areas of cross section in the ratio 2:1 if the same potential difference is applied across each wire in turn, what will be the ratio of current flowing in A & B ?
Answer : The ratio of the current flowing in wire A to wire B is **2:1**. --- ### Detailed Explanation Let's break down the problem using the relevant physics principles. #### 1. List the Given ... resistance, which is wire A. Our result confirms this: the current in A is twice the current in B....

Name any one material having a small value of temperature coefficient of resistance. Write one use of this material?
Answer : **Material:** **Manganin** (an alloy of copper, manganese, and nickel) **Use:** Due to its very low temperature coefficient of resistance, it is used to make ** ... for electrical measuring instruments like ammeters and Wheatstone bridges, where a stable and predictable resistance is essential....

If a wire is stretched to double its length. What will be its new resistivity?
Answer : The short answer is: **The new resistivity will be exactly the same.** --- ### The Detailed Explanation #### What is Resistivity? **Resistivity (ρ)** is an **intrinsic property** of a material. This ... 2) and area is halved (factor of 1/2). | Becomes **four times** the original resistance. |...

Draw the graph showing the variation of conductivity with temperature for a metallic conductor?
Answer : The conductivity for a metallic conductor decreases with the increase in temperature. ![][1] [1]: https://electrical-engineering.app/?qa=blob&qa_blobid=10491891827766109637 ### Explanation: The Physics Behind the Graph To understand this ... | **Low** |...

State one condition for maximum current to be drawn from the cell?
Answer : For maximum current to be drawn from a cell, the **external resistance in the circuit should be zero**. This condition is also known as a **short circuit**. **Explanation:** The current (I) drawn from a cell ... possible value is 0. When R = 0, the current is at its maximum value, I_max = E / r....

If potential difference V applied across a conductor is increased to 2V , how will the drift velocity of the electron change?
Answer : ### Short Answer If the potential difference V applied across a conductor is increased to 2V, the **drift velocity of the electrons will also double**. ### Detailed Explanation Let's ... the electric field, which doubles the force on the electrons, which doubles their average drift velocity....

If the temperature of a good conductor decreases, how does the relaxation time of electrons in the conductor change?
Answer : ### The Short Answer If the temperature of a good conductor decreases, the **relaxation time of electrons increases**. --- ### The Detailed Explanation To understand why, let's break ... **. This is why good conductors become even better conductors (less resistive) at lower temperatures....