Gravitational and electric fields Flashcards
In what way is T (period) related to r (orbital radius)?
T ² ∝ r ³
What is the equation for escape velocity?
v = √((2GM)/r)
What is gravitational potential energy?
The energy required to bring unit mass (1kg) from infinity to that point.
If the force between two charged objects in an electric field is attractive, is the force positive or negative?
Negative
If the force between two charged objects in an electric field is repulsive is the force positive or negative?
Positive
What is the meaning of E in terms of electric fields?
Electric field strength.
If a positivity charged particle is moving through an electric field, which direction will the force act in?
The same direction as the electric field lines.
If a negatively charged particle is moving through an electric field, which direction will the force act in?
The opposite direction to the electric field lines.
In terms of electric fields, what does V mean and what is the unit?
Absolute electric potential, Volt (V).
How would you draw a gravitational field around and object?
Vector lines pointing into the object from many directions which are equally spaced apart.
What is the relationship of the law of gravitation?
Follows the inverse square law: F ∝ 1/r²
If the distance between masses doubles, what will be the strength of the force of gravitation?
One quarter of the strength of the original force.
What is the unit of gravitational field strength, g?
N/kg (m/s²)
Is g a vector or a scalar?
A vector.
What is the shape of a gravitational field?
Radial.
What is gravitational potential?
The gravitational potential energy that a unit mass would have at a point.
What is the sign of gravitational potential and gravitational potential energy?
Negative.
What happens to the gravitational potential and gravitational potential energy as the distance from the body increases?
They become less negative.
What is the gravitational potential and gravitational potential energy at infinite distance from the body?
Zero.
what does the area under a gravitational field strength against distance graph give?
Change in gravitational potential.
What is gravitational potential difference?
The energy needed to move a unit mass.
When is work done in a gravitational field?
When moving against the force of gravity; when changing equipotentials.
How is the speed of a satellite related to its orbital radius?
The speed is inversely proportional to the square root of its orbital radius;
v ∝ 1/√r
How do you calculate the total energy of a satellite?
Kinetic energy + potential energy.
How does the total energy of a satellite vary?
It doesn’t, total energy is always constant.
How does the speed of a satellite change as it travels around an elliptical orbit?
It will speed up as its height decreases and vice versa.
What are geostationary satellites useful for?
Sending TV and telephone signals as you don’t need to alter the angle of your receiver or transmitter to keep up.
How high are low orbiting satellites?
Between 180-2000km above the Earth’s surface.
What are low orbiting satellites useful for?
Imaging, spying, monitoring the weather and communications although multiple satellites will be needed to maintain constant coverage.
Which parts of the Earth do low orbiting satellites cover?
All of it over multiple orbits.
Where must geostationary satellites be over the Earth in order to maintain their orbit?
Directly above the equator.
