Topic 4 - Electrical Potential Energy
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What happens when a ball drops from point A to B under gravity?
Gravity does work on the ball.
According to the work–energy theorem, what equals the kinetic energy gained by a falling object?
The work done by gravity.
According to conservation of mechanical energy, what equals the kinetic energy gained by a falling object?
The potential energy lost.
Do similar arguments about work and energy apply to electric forces?
Yes, similar arguments apply to electric forces.
What does EPE stand for?
Electrical Potential Energy.
What is the SI unit of Electrical Potential Energy?
Joules (J).
What is electric potential?
Electric potential is the potential energy per unit charge.
What is the SI unit of electric potential?
Volt (V).
What is a volt equivalent to in base units?
1V=1J/C.
How is electric potential at a point defined?
The electric potential energy of a small test charge divided by the magnitude of the charge.
What do we often talk about instead of absolute electric potential?
Potential difference.
In the example, what is the charge of the test charge?
+2.0 × 10(-6)C.
How much work is done by the electric force when the charge moves from A to B?
+5.0 × 10(-5) J.
What two things must be determined in this example problem?
Difference in electrical potential energy between A and B
Potential difference between A and B.
In the conceptual example, what happens to a positive test charge released at A?
It accelerates toward B.
What happens after the positive charge reaches B?
It continues accelerating toward C.
What assumption is made about motion in the conceptual example?
Motion is only possible along the line.
What question is asked about a negative test charge?
What will a negative test charge do when released from rest at B?
How does a positive charge move in an electric potential field?
It accelerates from higher electric potential to lower electric potential.
How does a negative charge move in an electric potential field?
It accelerates from lower potential to higher potential.
What is the simple analogy used to describe this behaviour?
Positive charge → rolls down
Negative charge → rolls up.
Why is a non-SI unit sometimes used for energy in electric potential problems?
To easily express energy changes for particles with charge ±e.
What is an electron volt (eV)?
The amount by which the potential energy of an electron changes when it moves through a potential difference of 1 volt.
What ion moves between points A and B in the example?
A Cu²⁺ ion.
What is the potential difference between A and B?
2 V.
What must be calculated for the Cu²⁺ ion?
The energy gained, expressed in eV and J.
What second ion is introduced in the problem?
A Mg²⁺ ion.
What comparison must be made between the Mg²⁺ ion and Cu²⁺ ion?
How much energy the Mg²⁺ ion gains compared to the Cu²⁺ ion.
What atomic masses are given?
Cu = 63.5 u
Mg = 24.3 u.
What is the mass of the particle in the example?
1,8 × 10(-5) kg.
What is the charge of the particle?
+0.3 × 10(-5) C.
From where is the particle released?
Point A.
In what direction does the particle accelerate?
Horizontally.
Where does the particle move to?
Point B.
What is the only force acting on the particle?
The electric force.
What is the electric potential difference between A and B?
Potential at A is 25 V greater than at B.
What must be found in part (a) of the problem?
The speed of the particle at point B.
What scenario is considered in part (b)?
The same particle has a negative charge and is released from point B.
What must be determined in part (b)?
The speed at point A.
What is applied across the gel in gel electrophoresis?
An electric field.
What materials can the gel be made from?
Polyacrylamide
Agarose.
Why does DNA move in an electric field?
DNA has phosphate groups with positive charge.
How do different DNA molecules move in the gel?
Different masses move at different rates.
What is gel electrophoresis used for?
Identifying and quantifying DNA.
How is the gel visualized after electrophoresis?
It is photographed under UV light.
What appears in the gel image?
Bands.
What are the bands compared to?
A reference sample with known composition.
What type of samples may appear in the gel?
Multicomponent samples.
What does the position of a band indicate?
The protein identity.
What does the brightness of a band indicate?
The quantity present.
What is neural impulse transmission an example of?
A biomedical application of electric potential.
What medical diagnostic tool is based on electrical signals in the body?
Electrocardiogram (ECG).
