Unit - 4 - Electric and Magnetic Fields

What is an electric field?

The space around a charged object in which another charged object experiences an electric force.

- The force acting upon is the same at any point.
- Electric fields are slightly different in that a charged particle will experience a force in this field, whether it is stationary or moving. (unlike magnetic fields)

What is Electrostatic Force?

The force between electrically charged objects (like charges repel and opposite charges attract each other).
- All charged particles create their electric fields.
- Force affecting another particle decreases as the distance increases.

What is Electric field strength?

The force experienced per unit positive charge at that point.
E = Nm-1

E = Nm-1

F = N

Q = CV

what is the acceleration of a particle formula?

a= (EQ/m)

E - electric field strength

Q - Charge

m - mass

What is Positive and Negative Point Charge?

Charge coming from a point, the farther away from the point, the lower amount of force applied.

They have equally spaced field lines

Positive point charge - the charge flows outwards

Negative point charge - the charge flows inwards

What type of field does a point charge create?

Radial Field

What is Coulomb's Law?

and what is the formula?

The electrostatic force between two point charges is proportional to the product of the charges and inversely proportional to the square of their separation.

what are the three electric field patterns?

two oppositely charged point electrodes

Two same charged point electrodes

Two oppositely charged plate electrodes

What is Electric Potential?

Potential energy per unit charge of a positive point charge at that point in a field.

E = VQ

E - electric field strength

V - voltage

Q - charge

What is potential difference?

the change in potential between 2 locations in a field.

kE = VQ

kE - kinetic energy

V - voltage

Q - charge

What do two charged parallel plates produce?

A uniform electric field between the plates.

F = EQ

W = Fd

W = VQ

E = V/D

What are equipotentials?

Positions within a field with zero p.d. between them.

What is Millikan's oil drop experiment?

Robert Millikan Developed a famous science experiment to determine the charge of an electron.

What is a capacitor?

Electrical component that can store charge and so, can be used as an energy store.

Consists of pair of plates with an insulator between them

How does a capacitor work?

-The plates are neutral until a source is connected.

-When the capacitor is connected to a cell, electrons flow from the cell.

-The current causes electrons to be moved from right plate to the left plate.

What makes up a capacitor?

Consists of flat metallic plates arranged parallel to one another.

It's an electrical component that can store char

What are the charges in a capacitor

They're of equal and opposite charge, so there is difference across the plates.

What happens to the current in the current when the voltage across the plates is equal to the emf of the cell?

current falls to 0

What is capacitance?

the amount of charge a capacitor can store per unit volt applied across it.

C - Farad (F)

Q - charge

V - voltage

How do you work out the capacitance from a Charge against time graph

Calculate gradient

How do capacitors behave in a parallel circuit?

The pd across each capacitor is them same, since they're in parallel.

Q = Q1 + Q2

using Q = VC

VC = VC1 + VC2

so

C = C1 + C2

What is Kirchhoff's second law?

the sum of all voltages around a loop is 0

How do capacitors behave in a series circuit?

Kirchoff's second law

states:

V = V1 + V2

Q = VC so

Q/C = Q1/C1 + Q2/C2

but Q = Q1 = Q2

so

1/C = 1/C1 + 1/C2

what does the graph Pd against time (charging and discharging) look like?

what does the graph charge against time look like?

What does the graph for current against time look like?

How do you charge a capacitor?

Battery provides a constant emf of V0

the maximum current in the circuit and the capacitor starts to charge up

the pd across capacitor increases from zero as it gathers charge

according to the kirchoff's law

V 0 = VC + VR

So VR decreases as VC increases

after a long time, depending on the time constant, capacitor will be fully charged and have a pd of V0 and VR will be zero.

What is the Charing equation for current (for voltage)?

The same formula works for current, replace the V for I