Electric charges and fields

 

Electric Charges and Fields

  
 Problems

Question1. Three-point charges of +2 μC, -3 μC, and -3 μC are kept at the vertices A, B, and C respectively of an equilateral triangle of the side of 20 cm as shown in the figure (a). What should be the sign and magnitude of the charge to be placed at the mid-point (M) of side BC so that the charge at A remains in equilibrium?



Question2. Calculate the electric field strength required to just support a water drop of mass 10-3 kg and having a charge of 1.6 × 10-19 C.

Solution. Here m = 10-3 kg, q = 1.6 × 10-19 C

Let E be the strength of the electric field required to just support the water drop. Then

Force on water drop due to electric field = Weight of water drop

Or                                  qE = mg

Question3. Calculate the voltage needed to balance an oil drop carrying 10 electrons when located between the plates of a capacitor which are 5 mm apart. The mass of oil drop is 3 × 10-16 kg. Take g = 10 ms-2.


Question4. How many electrons should be removed from a coin of mass 1.6 g, so that it may just float in an electric field of intensity 109 NC-1, directed upward?

Solution. Here m = 1.6 g = 1.6 × 10-3 kg,

                                                 E = 109 NC-1

Let n be the number of electrons removed from the coin,

Then charge on the coin,

                                                 q = + ne

When the coin just floats,

Upward force of electric field = Weight of coin

Or                                       qE      or      neE = mg

Question5. A pendulum of mass 80 milligrams carrying a charge of 2 × 10-8 C is at rest in a horizontal uniform electric field of 2 × 104 Vm-1. Find the tension in the thread of the pendulum and the angle it makes with the vertical.

Solution. Here m = 80 mg = 80 × 10-6 kg

        q = 2 × 10-8 C, E = 2 × 104 Vm-1



Question6. An electron moves a distance of 6 cm when accelerated from rest by an electric field of strength 2 × 104 NC-1. Calculate the time of travel. The mass and charge of the electron are 9 × 10-19 kg and 1.6 × 10-19 C respectively.

Solution. Force exerted on the electron by the electric field,

 


  Question7. An electron falls through a distance of 1.5 cm in a uniform electric field of magnitude 2.0 × 104 NC-1. Given in figure (a), the direction of the field is reversed keeping its magnitude unchanged and a proton falls through the same distance. Given in figure (b), compute the time of falls in each case. Contrast the situation (a) with that of ‘free fall under the gravity’.



Thus the heavier particle takes a greater time to fall through the same distance. This is in contrast to the situation of ‘free fall under gravity’ where the time of fall is independent of the mass of the body. Here the acceleration due to gravity ‘g’ being negligibly small has been ignored.


Question10. An electric field E is set up between the two parallel plates of a capacitor, as shown in the figure, an electron enters the field symmetrically between the plates with a speed v0. The length of each plate l. find the angle of deviation of the path of the electron as it comes out of the field.







                                  












Comments

Post a Comment

please do not enter any spam link in the comment box

Popular posts from this blog

FORCE AND LAWS OF MOTION, Class IX, Part 4

Image
  If a boy wearing roller skates stands facing a wall and pushes the wall with his hands, the boy finds himself moving backward, away from the wall. It appears as if the wall also pushes the boy away. When the boy exerts a force on the wall by pushing it with his hands, then the wall exerts an equal force on the boy in the opposite direction . Since the boy is wearing roller skates, the opposite force exerted by the wall makes him backward, the boy on roller skates is exerting force on the wall towards the left side. The wall exerts an equal force on the boy towards the right side. Due to this, the boy moves in the backward direction. From this discussion, we conclude that when a boy exerts a force on the wall, the wall exerts an equal and opposite force on the boy . This is just an illustration of Newton’s third law of motion. Whenever one body exerts a force on another body, the second body exerts an equal and opposite force on the second body. The force exerted by the first bo
Read more

FORCE AND LAWS OF MOTION, Class IX, Part 3

Image
                                         In order to understand Newton’s second law of motion, we should first know the meaning of the term momentum of a moving body (or moving object). We know that a cricket ball is much heavier than a tennis ball. Suppose we throw a cricket ball and a tennis ball, both with the same speed or velocity. It will be found that more force is required to stop the cricket ball (Which has more mass) and less force is required to stop the tennis ball (which has less mass). We conclude that the force required to stop a moving body is directly proportional to its mass. If we throw two cricket balls of the same mass at different speeds or velocities, it will be found that more force is required to stop that cricket ball which is moving with higher velocity and less force is required to stop that cricket ball which is moving with higher velocity and less force is required to stop the cricket ball moving with lower velocity. So conclude that the force required to
Read more

LIGHT, Class X,, MCQ Part 1

                                                               MCQ'S MCQ Questions for Class 10 Science Light Reflection and Refraction with Answers Students can solve NCERT Class 10 Science Light Reflection and Refraction Latest Exam Pattern Multiple Choice Questions with Answers to know their preparation level. Question1. When light falls on a smooth polished surface, most of it (a) is reflected in the same direction            (b) is reflected in different directions (c) is scattered                                                                                    (d) is refracted into the second medium                                                                          Answer: a                                                                                                                      Q2. The image formed by reflection from a plane mirror is                                                            (a) real and inverted                                       
Read more