**COULOMB’S LAW AND CHARGED PARTICLE IN ELECTRIC FIELD**

**OBJECTIVES:**

To verify the coulomb’s law

To study the motion of charge particle in electric field.

**PROGRAM:** https://ophysics.com/em1.html

**BACKGROUND**:

Charles Coulomb measured the magnitude of the electric force between charged objects using the torsion balance. He found that-

The electric force between wo pint charge is directly proportional to the product of absolute value of the charges. If charge is same the force is repulsive and if charges are opposite the force is attractive.

The electric force between two-point charges is inversely proportional to the square of the distance between the point charges.

From Coulomb’s experiment it can be seen that the electric force (sometime called the electrostatic force) between two-point charges (q1 and q2) is equal to

Fe =

Where, is the constant called Coulomb constant and has the value is SI unit as

= 8.987 6 x 109 N. m2/C2

can also be written as

= 1/4πε0

where, ε0 is called the permittivity of the free space and has value

ε0 = 8.854 2 x 10-12 C2/N. m2

Electric Field:

The electric field at a point is defined as the electric force acting on a positive test at that point.

E = Fe/q0

or Fe = q0E

The direction of electric field if from positive charge to negative charge.

Motion of charge particle in an electric field:

If a charge particle of mass ‘m’ and charge ‘q’ moves in an electric field, it experience a force

Fe = qE

If this is the only force acting on the particle then

Fe = qE = ma

The acceleration of the particle

a = qE/m

You may apply equation of motion to get the horizontal and vertical distance travel in electric field and the final velocity of the charge particle.

xf = xi + vxt

yf = yi + vyit + ½ ayt2

**PROCEDURE:**

Verify Coulomb’s Law

Open program https://ophysics.com/em1.html

Exercise 1

Set charge A = 10 x 10-4

Set Charge B = 10 x 10-4

Keep the distance between the charges = 5 m

Calculate the force between the two-charge particle using Coulomb’s law

Confirm your result using simulation. Include the screen shot of the simulation.

Exercise 2:

Keep charges constant and increase the distance between the charge particles and plot a graph force Vs. distance. What did you observe?

Exercise 3: Keep the distance between the charges same and one charge constant. Change another charge and plot a graph between F vs. charge. What did you observe?

Exercise 4: Motion of charge particle in electric field

Open program https://ophysics.com/em6.html

Set the following values

Voltage = 40 V

Distance between plates = 5 cm

Initial velocity = 8 x 105 m/s

Charge on particle = 0.3 μC

Mass of particle = 0.3 x 10-16 kg

Particle enter in the field at a vertical distance on 2.5 cm

Calculate how much time the particle will strike the plate (lower or upper?)

4.2 Horizontal distance travelled in this time.

4.3 Run the program and check your results obtained in calculations. Include the screen shot in the lab report.

4.4 What will happen if the polarity of charge will be opposite. Predict the result and run the simulation. Are the results same as you predicted? Include the screen shot in the lab report.