# Errors in Concepts of Physics by Dr HC Verma

**Disclaimer:** *The errors given here are neither reported to nor have the approval of the author or publishers. Primary objective of this page is to help the readers and the author. We have taken care in preparation of this list, but make no expressed or implied warranty of any kind and assume no responsibility for errors or omissions.*

## Volume 1

- Chapter 3: Rest and Motion: Kinematics, Exercise 44: "The benches of a gallery in a cricket stadium are..." Given answer is Sixth whereas it should be fifth. See detailed solution in PDF. (Error reported by
*Apratim Tripathi*).
- Chapter 10: Rotational Mechanics, Objective I, Question 19: "A person sitting firmly over a rotating stool has his arms..." Given answer is 2011 and old prints is (c) whereas it should be (b). It is corrected in 2015 print of the book. See detailed solution in PDF. (Error reported by
*Yash Zanwar* on www.quora.com).

## Volume 2

- Chapter 24: Kinetic Theory of Gases, Exercise 32: "A container of volume 50 cc contains air..." Given answer for part (a) is 0.058 g wheras it should be 0.063 g. See detailed solution in PDF (Error reported by
*Mrinal Durgesh*).
- Chapter 32: Electric Current in Conductors, Section 32.2 on Pg. 173: The formula for drift velocity given in Concepts of Physics (Vol 1) Sec 32.2 on Pg. 173 is
\begin{align}
v_d= \frac{1}{2}\left[\frac{eE}{m}\right] \tau
\end{align}
where $E$ is electric field and $\tau$ is average time between successive collisions (also called relaxation time). On the other hand, the formula given in NCERT Class 12 Part 2 Sec 3.5 Pg 98 Eqn 3.17 is
\begin{align}
v_d=\left[\frac{eE}{m}\right] \tau.
\end{align}
The confusion on drift velocity formula is not new. It was discussed by many authors like Bernhard Jakoby, Eur. J. of Phys.
**30** (2009) 1--12 (see eqn. 7 and 8 in this paper). The definition of drift velocity requires concepts from statistics (e.g, expected value, probability distribution etc.) which is generally not taught at school level. The formula given in NCERT is commonly accepted in physics community. However, it is mostly a matter of convention and does not affect the analysis. See this pdf for more. (Error reported by *Anonymous* on www.quora.com).
Here is an explanation by Dr HC Verma himself.
- Chapter 38: Electromagnetic Induction, Exercise 8: in "(b) the emf induced at $\tau=(\pi/900)s$", replace $\tau$ by $t$.