6.2 - Electric Force and field

6.2 – Electric Force and Field

Electric Forces simulations

http://phet.colorado.edu/en/simulation/balloons or CLICK ON THE PICTURE

Unlike Gravitational Fields with only one type of mass to act upon, Electric Fields have two types of charge that they can make an Electric Force on: POSITIVE and NEGATIVE.

http://phet.colorado.edu/en/simulation/travoltage or CLICK ON THE PICTURE

Use these two simulations to see how electric charges behave.Notice which one can move and which one can’t?

Charges (Q) – measured in Coulombs

The Law of Conservation of Charge (Q)

Charge can neither be created nor destroyed.

Electric FieldsAn electric field is a region of space where a charged object experiences a force due to its charge.

Field LinesBecause there are two charges that move in different directions in a field it has been decided that Field Lines should show the direction that a POSITIVE charge would accelerate if placed in the field.

Electric Fields (more examples)

The arrows are always showing the direction that a POSITIVE charge would move in the field.

Electric Fields simulations

http://phet.colorado.edu/en/simulation/electric-hockey

Electric Field HockeyCharges and Fields

http://phet.colorado.edu/sims/charges-and-fields/charges-and-fields_en.html Use these two simulations to see how the field lines work for different

charges.

Coulomb’s Law

𝐹=𝑘𝑄1𝑄2

𝑟 2

Newton’s Law

𝐹=𝐺𝑚1𝑚2

𝑟2

The Force between two point charges is directly proportional to the product of the CHARGES and inversely proportional to the square of their distance apart.

𝐹∝𝑚1𝑚2𝐹∝

1

𝑟 2𝐹∝𝑄1𝑄2 𝐹∝1

𝑟 2

The Force between two point masses is directly proportional to the product of the MASSES and inversely proportional to the square of their distance apart.

k= 9 x 10-9 Nm2C-2 G= 6.6742 x 10-11 m3kg-1s-2

Electric Field Strength

Definition:The force per unit charge experienced by a small positive test charge placed in the field.

Gravitational Field Strength

Definition:The force per unit mass experienced by a small test mass placed in the field.

𝐸=𝐹𝑄

𝑔=𝐹𝑚

Units: NC-1 Units: NKg-1

Example:

Electric Field around a sphere of charge Q

𝐸=𝑘𝑄𝑟 2

𝐸=𝐹𝑞

𝐹=𝑘𝑄𝑞𝑟2

Because Field Strength is a vector it can be added using Vector addition just like Gravitational Field Strength