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Physics 30 > Fields > Flashcards

Fields Flashcards

1
Q

Law of electric charges.

A

Like charges repel. Unlike charges attract.

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2
Q

Law of conservation of charge.

A

Charge can be transferred from one object to another, but the total charge of a closed system remains constant.

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3
Q

Elementary charge.

A

1.602*10^-19 C

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4
Q

Coulomb’s Law.

A

The force between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between the charges.

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5
Q

Where does an electric field exist?

A

Where a test charge placed would have a force exerted on it.

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6
Q

What are electric fields?

A

electric force / charge

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7
Q

What is field strength not dependent on when between two charged plates?

A

Distance from either plate. It is uniform between the two.

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8
Q

What is the unit for electric potential energy?

A

Voltage. (Joule per Coulomb)

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9
Q

What are the symbols for gravitational, electric and magnetic fields?

A

Gravitational: g
Electric: ε
Magnetic: B

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10
Q

How does the strength of fields and distance relate?

A

Inverse square law.

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11
Q

How did Newton explain gravity?

A

Mass attracts mass.

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12
Q

Paths of planets are…

A

Ellipses with the centre of the sun at one focus.

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13
Q

A line segment joining a planet and the sun…

A

Sweeps out equal areas during equal intervals of time.

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14
Q

Kepler’s Law.

A

k=R^3 / T^2
This constant applies to all orbits.

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15
Q

How much is 1 A.U?

A

1 astronomical unit is the average distance between the Earth and the Sun.

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16
Q

How did Einstein explain gravity?

A

Mass warps spacetime. This means that gravity is not a force. Objects trace geodesics (paths of least action through spacetime) unless acted on by a net external force.

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17
Q

What is the principle of equivalence?

A

Absence of a gravitational field (true weightlessness) is indistinguishable from free fall acceleration (apparent weightlessness).

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18
Q

Do neutral objects (not particles) attract to charged objects?

A

Yes. A positive charge will attract negative charges within an object create an imbalance and attraction. A negative charge will repel negative charges within an object creating an imbalance and attraction.

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19
Q

What are the ways to build electrostatic charge?

A

Friction. Conduction. Induction.

20
Q

What determines the quantity of charge on an object?

A

The number of elementary particles on the object multiplied by the elementary charge (e)

q=Ne

21
Q

What is an electric field?

A

A region surrounding a charge that exerts a force on charges within the field.

22
Q

What is direction in an electric field?

A

The direction that a positive charge will move.

23
Q

What is electric potential difference?

A

Voltage.

24
Q

Do electric and/or magnetic fields need both poles?

A

Electric fields can have 1 pole.
Magnetic fields always have two.

25
Q

What are the units for magnetic fields?

A

Teslas (T)
N/(Cm/s)

26
Q

What rule do you use to determine the direction of force on a charge moving through a magnetic field?

A

Right hand rule for positive charges.
Left hand rule for negative charges.

27
Q

How do you determine the magnetic field direction around a wire?

A

Right hand rule #2.

Point thumb in direction of conventional current. Curl fingers. Direction fingers move in is direction of magnetic field.

28
Q

What is mass spectrometry?

A

An analytical technique that identifies the chemical composition of a compound or a sample based on the mass to charge ratio of the charged particle.

29
Q

What is current?

A

The flow of charges. Amperes (I).
I=C/s

30
Q

What is a solenoid?

A

A coil of wires. When current flows through it, it becomes an electromagnet.

31
Q

How does velocity proportionally relate to radius of orbit around the Sun?

A

Velocity drops off at an inversely proportional rate.

32
Q

How does velocity of orbit change with radius of orbit around a galaxy?

A

It does not appear to change.

33
Q

How can the Sun’s mass be estimated?

A

Using a planets orbit and speed.

34
Q

Why does measuring the mass of galaxies using the brightness method get less than using the orbital method?

A

There must be a large amount of unseen mass.

35
Q

Observations that indicate dark matter have been found in…

A

Every galaxy that has been examined.

36
Q

Evidence for dark matter comes from…

A

Orbits of the stars and gravitational lensing.

37
Q

Mass found by gravitational lensing method agrees with…

A

Orbital method

38
Q

Why is dark matter called “dark”?

A

It does not emit or reflect any radiation.

39
Q

What do most physicists think dark matter is made of?

A

WIMPs or Axions.

40
Q

How much is known about dark matter?

A

There are some ideas about it which are currently being tested.

41
Q

What is motor force?

A

The force that a magnet exerts on a current-carrying conductor. F=ILB*sin(ϴ)

42
Q

What happens with parallel conductors?

A

They either attract or repel each other depending on their directions of current. Same direction, attraction. Opposite direction, repulsion.

43
Q

What is Ampere’s law?

A

The cable’s internal magnetic field, B, is directly proportional to the current, I, and inversely proportional to the circumference.
B=μI / 2πr

44
Q

What happens when a charged object touches a neutral object?

A

Electrons transfer between them to balance out. Ex: A positive object will take some electrons, making the neutral object positive as well. A negative object will give some electrons, making the neutral object negative as well.

45
Q

What is electric potential energy?

A

The energy stored in the system of two charges a certain distance apart.

Physics 30 (6 decks)

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