Electric field Lesson

Electric field

​Chrisbania Vargas

​An area of influence around a charged object.
The magnitude of the field is proportional to the amount of electrical force exerted on a positive test charge placed at a given point in the field.

​Electric field

The electric field around a charged object is a vector and can be represented with electric field lines that point in the direction of the force exerted on a unit of positive charge. In other words, electric field lines point away from a positive charge and toward a negative charge, as shown in the diagram.

Electric field

Electric field

Electric field = electric force = E= F
test charge q₀

The SI unit of electric field is the newton per coulomb (N/C).

Multiple Choice

What is the unit of electric field?

• A) Newton (N)

• B) Coulomb (C)

• C) Newton per Coulomb (N/C)

• D) Volt (V)

Multiple Choice

Which of the following statements is true about the direction of the electric field?

• A) The electric field points toward positive charges.

• B) The electric field points away from negative charges.

• C) The electric field points away from positive charges.

• D) The electric field points in random directions.

Multiple Choice

The electric field produced by a point charge is inversely proportional to:

• A) The square of the distance from the charge.

• B) The distance from the charge.

• C) The charge itself.

• D) The charge's mass.

As Courtney switches on the TV set to watch her favorite cartoon, the electron beam in the TV tube is steered across the screen by the field between two charged plates. If the electron experiences a force of 3.0 106 N, how large is the field between the deflection plates?

As Courtney switches on the TV set to watch her favorite cartoon, the electron beam in the TV tube is steered across the screen by the field between two charged plates. If the electron experiences a force of 3.0 106 N, how large is the field between the deflection plates?

​E = F/q_o

= (3.0 10^-6 N)/(1.60 10^-19 C)

= 1.9 10¹³ N/C

Multiple Choice

A charged particle experiences a force of 4.0×10⁻⁶N as it moves through an electric field. If the particle has a charge of 2.0×10⁻¹⁹ C, what is the magnitude of the electric field?

• 2.0×10^-25N/C.

• 2.0×10¹³N/C.

• 6.0×10¹³N/C.

• 2.0×10^-13N/C.

For a point charge (or other spherical charge distribution), the magnitude of the electric field can be written as

E = F = kq_oq = kq
q₀ q_od² d²

​where q is the charge on the surface of the object, and d is the distance between the center of the charged object and a small positive test charge, q_o, placed in the field.

Multiple Choice

Which of the following is the formula for the electric field produced by a point charge?

• A) E=kq/r

• B) E=kq/r²

• C) E=q/r2

• D) E=qr/k

Valery pulls her wool sweater over her head, which charges her body as the sweater rubs against her cotton shirt.
a) What is the electric field at a location where a 1.60x10^-19 C-piece of lint experiences a force of 3.2x10^-9 N as it floats near Valery?
b) What will happen if Valery now touches a conductor such as a door knob?

Valery pulls her wool sweater over her head, which charges her body as the sweater rubs against her cotton shirt.
a) What is the electric field at a location where a 1.60x10^-19 C-piece of lint experiences a force of 3.2x10^-9 N as it floats near Valery?
b) What will happen if Valery now touches a conductor such as a door knob?

​a. Given: q₀ = 1.60x10^-19C Unknown: E = ?
F = 3.2x10^-9 N

Solved: E = F/q₀ = 3.2x10^-9 N / 1.60x10^-19 N = 2.0x10¹⁰N/C

Valery pulls her wool sweater over her head, which charges her body as the sweater rubs against her cotton shirt.
a) What is the electric field at a location where a 1.60x10^-19 C-piece of lint experiences a force of 3.2x10^-9 N as it floats near Valery?
b) What will happen if Valery now touches a conductor such as a door knob?

​b. She will reduce her charge in a process called grounding, in which excess electrons flow from her body into the ground and spread evenly over the surface of Earth.