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# physics.pptx

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# physics.pptx

Useful for class 12

Useful for class 12

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### physics.pptx

1. 1. CROSS FIELD AND ITS APPLICATION IN DETERMINATION OF SPECIFIC CHARGE
2. 2. HELLO! 1)SADEEP KHANAL 2)SHRISTI TAMANG 3)SHRADDHA POKHAREL 4)SANYAM KOTHARI 2
3. 3. WE ARE REALLY THANKFUL TO OUR PHYSICS TEACHER MR.SUSHIL UPRETI SIR AND HOD PHYSICS MR.DEVENDRA KHADKA FOR THEIR CONTINUOUS HELP AND SUPPORT. 3 ACKNOWLEDGEMENT
4. 4. CONTENTS; ✘ ELECTRIC FIELD AND MAGNETIC FIELD ✘ CROSS FIELD ✘ SPECIFIC CHARGE ✘ J.J. THOMSON EXPERIMENT ✘ CONCLUSION ✘ REFERENCES 4
5. 5. ELECTRIC FIELD Electric field is defined as the electric force per unit charge. The direction of the field is taken to be the direction of the force it would exert on a positive test charge. The electric field is radially outward from a positive charge and radially in toward a negative point charge. 5
6. 6. MAGNETIC FIELD A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to the magnetic field. 6
7. 7. CROSS FIELD ★ The uniform electric and magnetic fields acting mutually perpendicular to each other is called cross field. ★ The magnitude and direction of both fields are so adjusted that the deflection produced by one field on charged particle is cancelled by the deflection produced by the other. 7
8. 8. DETERMINATION OF VELOCITY IN CROSS FIELD Consider a beam of electron is moving with the velocity v in the electric field ‘E’ and magnetic field ‘B’. The force on electron due to electric field is Fₑ = eE . 8 The force on electron due to magnetic field is Fₘ =Bev When the beam is undeflected, then magnetic force (Fₘ) = electric force (Fₑ) Bev = eE or, v = E/ B .
9. 9. SPECIFIC CHARGE ★ The ratio of charge of electron to its mass is called as specific charge. ★ It is denoted by e . ★ It can be determined by using JJ Thomson experiment. 9 m
10. 10. J.J. THOMSON EXPERIMENT DETERMINATION OF SPECIFIC CHARGE 10
11. 11. J.J THOMSON EXPERIMENT 11 ★ The set up consists of a discharge tube with fluorescent screen. There are two electrodes: cathode ‘C’ and anode ‘A’. ★ A uniform electric field ‘E’ is applied in downward direction through the two horizontal metal plates P and Q. ★ A uniform magnetic field ‘B’ is applied in inward direction and is perpendicular to the electric field. ★ When the high voltage is applied between cathode and anode, a narrow beam of cathode rays is emitted from cathode to anode. This beam is allowed to pass between two plates ‘P’ and ‘Q’ and then strikes the fluorescent screen and luminous spot is seen. When both electric and magnetic fields are not applied, the beam of cathode rays moves straight and strikes at the centre 'O' of the screen.
12. 12. 12
13. 13. DETERMINATION OF SPECIFIC CHARGE 13 When sufficient amount of potential (V) is applied between the two electrodes electrons emitted from the cathode accelerate with velocity ‘v’ then, When the charge particle moves under the action of electric field strength (E) it moves towards the +ve plate and finally incident at point O, at fluorescent screen. In case of applying magnetic field only, the charge particle deviate and finally incident . If both magnetic and electric field are applied and their magnitude and direction is adjusted so that the charged particles move without deviation. At this condition charge particle incident at point O at the fluorescent screen, Then, We have,
14. 14. 14 Where, B is magnetic field strength. In this case the direction of magnetic field is perpendicular to the direction of the motion of the charged particle. From equation (i) and (ii), We get, Hence, the specific charge at the electron is determined if the values of E, B and V are known. The experimentally obtained specific charge of the electron is 1.7 ✕ 10¹¹ C/kg.
15. 15. CONCLUSION 15 In conclusion, this presentation helped us build our skills and expand our knowledge. We hope it also taught you something new about these topics. We would like to thank Sushil Sir and our classmates for their patience during our presentation.