This question is about the velocity selector shown in figure. Explain why ions travelling with a speed greater than your answer to part (b) will not emerge from the slit.

Magnetic force is greater than electric force. So, the ion travels in an upward curved path (towards the positive plate) and hence misses the slit S.

Explain how crossed E → and B → fields serve as a velocity selector.

A velocity selector is an arrangement of electric and magnetic field so that the charge of a particular velocity moves undeflected in electric and magnetic field. We know that, a stationary charged particle experiences a force F in an electric field only but a moving charged particle experiences a force both in electric E and magnetic field B . This is called the Lorentz force, given by: F → = q E → + v → × B → ....(i) Let the electric field vector, magnetic field vector and velocity vector be mutually perpendicular as shown in the figure drawn above. Hence, these can be written as: E → = E j ^ ; B → = B k ^ ; v → = v i ^ Hence, the force due to the electric field can be written as: F → E = q E → = q E j ^ ......(ii) Force due to the magnetic field can be written as: F → B = q v → × B → = q v i ^ × B k ^ = - q v B j ^ ....(iii) From (ii) and (iii), it is clear that the electric and magnetic fields are opposite in direction. If the magnitude of electric and magnetic fields are so adjusted that they become equal then the total force on the charge is zero and the charge with the velocity v will move deflected. Hence, the condition for the charge to move undeflected is: q E = q v B ⇒ v = E B .......(iv)

E M B I B E

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 7 - Moving Charges and Magnetism>Exercise

Embibe Experts Solutions for Chapter: Moving Charges and Magnetism, Exercise 1: Exercise

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Embibe Experts Physics Solutions for Exercise - Embibe Experts Solutions for Chapter: Moving Charges and Magnetism, Exercise 1: Exercise

Attempt the practice questions on Chapter 7: Moving Charges and Magnetism, Exercise 1: Exercise with hints and solutions to strengthen your understanding. Physics Crash Course (Based on Revised Syllabus-2023) solutions are prepared by Experienced Embibe Experts.

Questions from Embibe Experts Solutions for Chapter: Moving Charges and Magnetism, Exercise 1: Exercise with Hints & Solutions

HARD

12th Andhra Pradesh Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 7 - Moving Charges and Magnetism>Exercise>Q 21

What is velocity selector?

HARD

12th Andhra Pradesh Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 7 - Moving Charges and Magnetism>Exercise>Q 22

What are the limitations of a velocity selector?

HARD

12th Andhra Pradesh Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 7 - Moving Charges and Magnetism>Exercise>Q 23

Mention some applications of velocity selector.

HARD

12th Andhra Pradesh Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 7 - Moving Charges and Magnetism>Exercise>Q 24

This question is about the velocity selector shown in figure.

Question Image

State the directions of the magnetic and electric forces on a positively charged ion travelling towards the slit $S$ .

HARD

12th Andhra Pradesh Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 7 - Moving Charges and Magnetism>Exercise>Q 25

This question is about the velocity selector shown in figure.

Question Image

Calculate the speed of an ion emerging from the slit $S$ when the magnetic flux density is $0.30 T$ and the electric field strength is $1.5 \times 10^{3} V m^{- 1} .$