# OCR Advancing Physics: Electric Fields

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• Created by: Caraa
• Created on: 03-06-13 22:18
What is electric charge measured in?
Coulombs
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What is coulomb's law?
F (The force of attraction or repulsion between two charges) = kQq / r^2
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If the force is attractive is F positive or negative?
Negative
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If the force is repulsive is F positive or negative?
Positive
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What is the relationship between the forces on Q and q?
Equal and opposite
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What is electric field strength and how can it be calculated?
It is force per unit positive charge (The force that a charge of +1C would experience if it was placed in the electric field) and the equation E = F/q can be used to calculate it.
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What is the equation for electric field strength?
E = kQ/ r^2
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How would you draw the electric field lines in a radical field?
Imagine that a small +ve charge is put near the field. The field lines go in the direction the charge would move
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What is the electric potential energy at what is it's equation?
The work that would need to be done to move a small charge q from infinity to a distance r away from Q. EPE = kQq/r
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What electric potential energy would a charge an infinite distance away from Q have?
Zero
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In an attractive field what happens the the electric potential energy of g as r increases?
It gains electric potential energy
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In an replusive field what happens the the electric potential energy of g as r increases?
It loses electric potential energy as you have to do work against the repusion
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What is electric potential and what is the equation for it?
Electric potential energy per unit positive charge. V = EPE / q or V = kQ/r
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In a uniform field such as between two plates, what is the equation for field strength?
E = V/d
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What is the equation for the force acting on a charge moving through a magnetic field?
F = qvB
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Why are charged particles moving in a magnetic field deflected in a circular path?
Due to the left hand rule the force is perpendicular to the motion, meaning a circular path.
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What equation can you use for the radius of charged particle in a magnetic field?
r = mv/Bq
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What is stokes law?
F = 6.Pi.viscosity.r.v
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What are the forces acting on a oil drop before a electric field is involved?
The weight and viscous force
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When does the drop reach its terminal velocity (when will it stop accelerating)?
When weight and viscous force are equal
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What does the weight and viscous force being equal mean?
4/3.pi.r^3.p.g = 6.pi.viscosity.r.v (since mass = volume.density) and so r^2=9.viscosity.v/2.p.g so by measuring viscosity and p in separate experiments Millikan could calculate r
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Explain what happened when Millikan turned on the electric field?
He adjused the pd so the drop was stationary and hence viscous force was 0. Now only the force due to the electric field acts upwards.
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What do you get when you combine the equations E = F/q and E = V/d to find the electric force?
F = QV/ d
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Since the drop is stationary what does this mean the equation is?
QV/d = 4/3.pi.r^3.p.g meaning the only unknown is now Q
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What conclusion did Millikan come to?
He found the charge on many drops and noticed that the charge was always a multiple of 1.6x10^-19 so charge is 'quantised' (It exists in discrete packets i.e electrons)
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## Other cards in this set

### Card 2

#### Front

What is coulomb's law?

#### Back

F (The force of attraction or repulsion between two charges) = kQq / r^2

### Card 3

#### Front

If the force is attractive is F positive or negative?

#### Back ### Card 4

#### Front

If the force is repulsive is F positive or negative?

#### Back ### Card 5

#### Front

What is the relationship between the forces on Q and q?

#### Back 