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Physics > Electrical Physics > Flashcards

Electrical Physics Flashcards

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1
Q

Like charges…

A

Repel

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2
Q

Unlike charges

A

Attract

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3
Q

Can charge be created or destroyed?

A

No, it is only ever transfered from one object to another.

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4
Q

What does an electrostatic charge involve?

A

An imbalance of positive and negative charges.

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5
Q

Are the charges on a proton and electron equal?

A

Yes, they are however opposite in sign.

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6
Q

What happens when a charged object is placed near a conductor?

A

An opposite charge will be induced on the side of the conductor nearer the charge and a like charge on the side further away from the charge.

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7
Q

Coulumbs law for the force between two charges q1 and q2 at a distance of r is :

A

F=kq1q2/r2(squared)

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8
Q

The electric field E in any region of space is the ecectric force per unit of charge in that space. The equation is…

A

E=F/q

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9
Q

The force on acharge q in an electric field is given by…

A

F=qE

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10
Q

What does a battery establish is a conductor connected to its terminals?

A

An electric field.

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11
Q

What is the direction of an electric current?

A

The direction of transfer of the positive charge.

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12
Q

What does a source of EMF give charges?

A

Electrical potential energy

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13
Q

What is a potential diference?

A

The loss of potential energy per unit charge as charge flows through a circuit element.

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14
Q

What equation is used for energy lost?

A

E=qV

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15
Q

What does the current-potential difference relationship for an electrical device describe?

A

The electrical behaviour of the device.

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16
Q

What is matter made up of?

A

Vast numbers of positive and negative charges (protons and neutrons)

17
Q

What does the current-potential difference relationship for an electrical device describe?

A

The electrical behaviour of the device.

18
Q

What is Ohm law?

A

The cureent is directly proportional to the voltage.

19
Q

What is a device with a linear I-V graph known as?

A

An ohmic conductor. It obeys Ohm law

20
Q

Is the current in an non-ohmic conductor directly proportional to the voltage that is is dependant on?

A

No

21
Q

What is the resistance of a conductor defined as?

A

The ratio of the potential difference to the current, thus V=IR.

22
Q

Is the resistance of a ohmic conductor constant?

A

Yes

23
Q

How does the current flow in a metal?

A

Because of the potential difference along it.

24
Q

What does the amount of current that can flow through a material depend on?

A

The field, the cross sectional area and the length as well as the nature and temperature of the material.

25
Q

What is the resitance of a conductor given by?

A

R=pL/A where p is resistivity

26
Q

What can potential energy stored when charge is concentrated be converted to?

A

Other forms of energy or in man made devices.

27
Q

The rate at which energy is releasesd is given by?

A

The product of the potential (voltage) and the current P=VI. In SI units 1 watt is equal to 1 volt x 1 ampere 1W=1AV

28
Q

Total energy produced is given by?

A

E=Pt

29
Q

What is the direction of an EMF?

A

It can be constant which gives rise to a direct current DC.

Or it can be alternating which gives rise to alternating current AC.

30
Q

Why is power transmitted to cities at a high voltage?

A

In order to keep the current needed relatively low.

31
Q

What does an electric circuit normally consist of?

A

A source of EMF, conductors to carry current with little loss of energy, and circuit elements which turns the potential energy of the charges into some form of useful energy.

32
Q

In any electrical circuit the sum of all the currents flowing into any point is equal to?

A

The sum of the currents flowing out of it.

33
Q

The sum of all EMF values around a circuit is equal to?

A

The sum of all potential drops around the circuit.

34
Q

All circuits are combinations of?

A

Circuit elements in series or in parallel.

35
Q

In a simple series circuit the total voltage drop is the sum of?

A

The individual drops.

36
Q

In a simple parallel circuit the same voltage drop occurs across both elements. The total current that flows is the sum of?

A

The two individual currents.

37
Q

How does a source of EMF create electrical potential energy?

A

It uses some form of energy. Batteries use chemical energy. Generators use mechanical energy.

38
Q

If several sources of EMF are combined in series, the total EMF will be given by the sum of?

A

The individual sources.

39
Q

Sources of EMF should only be combined in parallel if?

A

They provide the same voltage. Cells in such a battery only need to provide half the current they would otherwise.

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