AIATS MEDICAL PHYSICS OYM TEST 0229 09 24 Q 01 05

Summary

In this video, Shubham Swami, a physics faculty at Aakash, provides detailed solutions for the ATS 2025 OVA-M Test 2, conducted on September 29, 2024. The video covers various physics concepts such as the average velocity of free electrons in a conductor, Ohm's Law, circuit resistance, and terminal potential difference across cells. The instructor explains each question with clarity, verifying the correct answers through calculations and logical reasoning. This comprehensive explanation helps students grasp complex topics in physics, with an emphasis on problem-solving techniques.

Takeaways

• 😀 The average velocity of free electrons in a conductor, in the absence of an external electric field, is zero due to their random motion.
• ⚡ Increasing the external electric field in a conductor increases the current density linearly, as per Ohm's law.
• 🔌 In a specific circuit, three resistors are connected in parallel, leading to an equivalent resistance of 8/3 ohms.
• 🔋 In a circuit with two cells, if one cell is discharging, its terminal potential decreases, while a charging cell's terminal potential increases.
• 📉 The exact values for terminal potential differences between two points (V1 and V2) in the given circuit come out to be 3 volts each.
• 📏 When comparing two wires of different diameters (D and D/4) but the same material, the drift velocity of electrons in the thinner wire is found to be 32 times that of the original wire.
• 🔧 Ohm's law and the relationship between current, electron density, and drift velocity help solve problems related to varying wire dimensions and current.
• 📊 The net resistance of the circuit between points A and B is calculated based on the parallel combination of resistors.
• 🔄 The relationship between external electric field and current density can be expressed as J = sigma * E.
• 📐 In solving for drift velocity in varying wire conditions, area and current changes play a critical role in determining the new drift velocity.

Q & A

Question 1: What is the average velocity of free electrons in a conductor in the absence of an external electric field?

The average velocity of free electrons in the absence of an external electric field in a conductor is zero due to the random motion of the electrons.

Question 2: What happens to current density when the value of the applied external electric field is increased at constant temperature?

When the value of the applied external electric field is increased at constant temperature, the current density increases linearly. This is known as Ohm's Law, which is represented by the equation j = σE, where j is current density, σ is conductivity, and E is the electric field.

Question 3: How is the equivalent resistance of a parallel circuit determined between points A and B?

In the given circuit, the resistors are connected in parallel, and the equivalent resistance between points A and B is calculated as 8/3 ohms. This is because the three resistors connected in parallel have a combined equivalent resistance of 2/3 ohms, which is added to the 2-ohm resistor.

Question 4: What happens to the terminal potential difference across a cell when it is discharging or charging?

When a cell is discharging, its terminal potential difference decreases, while when a cell is charging, the terminal potential difference increases.

Question 5: What are the values of terminal potential differences v1 and v2 for the two cells in the given circuit?

For the given circuit, the terminal potential difference across cell 1 (v1) is 3 volts, and across cell 2 (v2) is also 3 volts. This makes option 4 the correct answer.

Question 6: What is the relationship between current and drift velocity in a wire?

The relationship between current (I) and drift velocity (v_d) is given by the equation I = nAev_d, where n is the number density of electrons, A is the cross-sectional area of the wire, e is the charge of an electron, and v_d is the drift velocity.

Question 7: How does the drift velocity of electrons change if the diameter of the wire is reduced and the current is increased?

When the diameter of the wire is reduced by a factor of 4 and the current is doubled, the drift velocity of the electrons increases by a factor of 32.

Question 8: How do you calculate the equivalent resistance of resistors connected in parallel?

The equivalent resistance of resistors connected in parallel can be calculated using the formula 1/R_eq = 1/R1 + 1/R2 + 1/R3, where R1, R2, and R3 are the individual resistances. The result is the inverse of the sum of the reciprocals of the resistances.

Question 9: What is the vector form of Ohm’s Law?

The vector form of Ohm’s Law is given by the equation j = σE, where j is the current density, σ is the conductivity, and E is the electric field.

Question 10: How do resistors behave when they are at the same potential?

When resistors are at the same potential, they are considered to be connected in parallel, which affects how their equivalent resistance is calculated.