Electric ForcesElectric ForcesPhysics AStatic #3

Learning Targets0I can attribute the change in the electric force between

charged objects with the changes in the distance between them and/or the magnitude of the charges.

0I can calculate the electric force between two charged objects when given the charges of the objects and the distance between them.

0I can explain why acquiring a large excess static charge affects your hair.

Force as a Vector Quantity0The electrical force is expressed using the unit Newton. 0Being a force, the strength of the electrical interaction

is a vector quantity that has both magnitude and direction. 0The direction of the electrical force is dependent upon

whether the charged objects are charged with like charge or opposite charge.

Force as a Vector Quantity0Electrical force has a magnitude or strength. 0Electric force can be altered by changing three

variables. 0First, the quantity of charge on one of the objects

will affect the strength of the repulsive force. 0The more charged a balloon is, the greater the repulsive

force.

Force as a Vector Quantity0Second, the quantity of charge on the second object

will affect the strength of the force. 0Finally, the distance between the two objects will

have a significant and noticeable effect upon the repulsive force. 0The electrical force is strongest when the objects are closest

together. 0The magnitude of the force and the distance between the two

objects is said to be inversely related.

Coulomb’s Law Equation0Coulomb's law states that the electrical force between two

charged objects is directly proportional to the product of the quantity of charge on the objects and inversely proportional to the square of the separation distance between the two objects.

0The symbol k is a proportionality constant known as the Coulomb's law constant.

0The value is approximately 9.0 x 109 N • m2 / C2.

F =kqaqbd2

Coulomb’s Law Equation0The Coulomb's law equation provides an accurate

description of the force between two point charges.

0The symbols q1 and q2 represent the quantities of charge on the two interacting objects. 0Since an object can be charged positively or

negatively, these quantities are often expressed as "+" or "-" values.

0DO NOT USE THE “+” OR “-” VALUES IN THE EQUATION!

Suppose that two point charges, each with a charge of +1.00 Coulomb are separated by a

distance of 1.00 meter. Determine the magnitude of the electrical force of repulsion between them.

Two balloons are charged with an identical quantity and type of charge: -6.25 nC. They are held apart at a separation distance of 61.7 cm.

Determine the magnitude of the electrical force of repulsion between them.

Two balloons with charges of +3.37 µC and -8.21 µC attract each other with a force of 0.0626 Newton. Determine the separation distance

between the two balloons.

Comparing Electrical and Gravitational Forces

0Electrical force and gravitational force are the two non-contact forces.

0How are they similar?

Felect =kqaqbd2

Fgrav =Gm1m2d 2

k=9.0 *109 N *m 2 / C2 G=6.67*10−11N *m 2 / kg2

The Q in Coulomb's law equation stands for the _____.

a. mass of a charged objectb. # of excess electrons on the objectc. the current of a charged objectd. the distance between charged objectse. charge of a charged object

The symbol d in Coulomb's law equation represents the distance from ___.a. A to Bb. A to Dc. B to Cd. B to De. C to Df. A to Gg. B to Fh. C to E

Determine the electrical force of attraction between two balloons that are charged with the opposite type of charge but the same quantity of charge. The charge on the balloons is 6.0 x 10-7 C and they are separated by a distance of 0.50 m.

Joann has rubbed a balloon with wool to give it a charge of -1.0 x 10-6 C. She then acquires a plastic golf tube with a charge of +4.0 x 10-6 C localized at a given position. She holds the location of charge on the plastic golf tube a distance of 50.0 cm above the balloon. Determine the electrical force of attraction between the golf tube and the balloon.

A balloon with a charge of 4.0 µC is held a distance of 0.70 m from a second balloon having the same charge. Calculate the magnitude of the repulsive force.

At what distance of separation must two 1.00-microCoulomb charges be positioned in order for the repulsive force between them to be equivalent to the weight (on Earth) of a 1.00-kg mass?

Cause & Effect Relationships0Careful observation and measurement might

indicate that a pattern exists in which an increase in one variable always causes another measurable quantity to increase. 0This type of cause-effect relationship is described as

being a direct relationship. 0In electrostatics, the electrical force between two

charged objects is directly related to the magnitude of charge of the two objects.

0Increasing the charge of the objects increases the force of attraction or repulsion between the objects.

Cause & Effect Relationships0Observation might also indicate that an increase

in one variable always causes another measurable quantity to decrease. 0This type of cause-effect relationship is described as

being an inverse relationship.0In electrostatics, the electrical force between two

charged objects is inversely related to the distance of separation between the two objects.

0Increasing the separation distance between objects decreases the force of attraction or repulsion between the objects.

Cause & Effect Relationships0Electric force is very sensitive to distance.0The pattern between electrostatic force and distance

can be further characterized as an inverse square relationship. 0The factor by which the electrostatic force is changed is

the inverse of the square of the factor by which the separation distance is changed.

0 If the separation distance is doubled, then the electrostatic force is decreased by a factor of four (22).

0 If the separation distance is tripled, then the electrostatic force is decreased by a factor of nine.

Two charged objects have a repulsive force of 0.10 N. If the charge of one of the objects is doubled, then what is the new force?

Two charged objects have a repulsive force of 0.10 N. If the charge of both of the objects is doubled, then what is the new force?

Two charged objects have a repulsive force of 0.10 N. If the distance separating the objects is doubled, then what is the new force?

Two charged objects have a repulsive force of 0.10 N. If the distance separating the objects is tripled, then what is the new force?

Two charged objects have an attractive force of 0.10 N. If the distance separating the objects is quadrupled, then what is the new force?

Two charged objects have a repulsive force of 0.10 N. If the distance separating the objects is halved, then what is the new force?

Two charged objects have a repulsive force of 0.10 N. If the charge of one of the objects is doubled, and the distance separating the objects is doubled, then what is the new force?

Two charged objects have a repulsive force of 0.10 N. If the charge of both of the objects is doubled and the distance separating the objects is doubled, then what is the new force?

Two charged objects have an attractive force of 0.10 N. If the charge of one of the objects is tripled and the distance separating the objects is tripled, then what is the new force?