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Basic Physics > Electric current > Flashcards

Electric current Flashcards

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1
Q

What is an electric current (I)?

What is the formula, and the base unit?

A

The collective motion of particles carrying electric charge.

I = delta q (charge) / delta time.

Ampere, or C/s.

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2
Q

What is a conductor?

A

A material that contains charge carriers which can move freely.

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3
Q

What is an insulator?

A

An insulator is a material with no freely moving charge carriers.

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4
Q

What is a direct current (DC)?

A

A direct current is the current constant in time.

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5
Q

What is an alternating current (AC)?

What is the direction of the current?

A

An AC is when the current changes as a sine function over time.

The direction is defined according to the flow direction of the positive charges.

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6
Q

A. What does electric current flowing in a conductor depend on?

B. What does the speed of their collective motion depend on?

A

A. It depends on the strength of the electric field moving the charge carriers.

E.g. voltage.

B. Their speed of the charges depend on the resistance of the material.

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7
Q

What is Ohm’s law?

A

The electric current (l) in a conductor is proportional to the voltage (U) between two poles:

U = R/I.

R is a constant, does not depend on the voltage.

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8
Q

What is electric resistance?

What is the SI unit?

A

The ration of voltage (U) between two poles of a conductor and the current (l) flowing through it.

R= U/I.

Ohm.

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9
Q

What does resistance of a conductor depend on?

A

It depends on the conductor’s dimensions and material properties.

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10
Q

What happens if the conductor is long(er)?

A

The same voltage corresponds to a weaker electric field and the motion of charges will be slower and the electric current lower - the resistance will be greater.

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11
Q

A. What happens if the cross-sectional area of a conductor is greater?

B. What is the formula and what is it called?

A

A. The more charge carriers can pass for a given voltage and electric field strength, so the current will be higher and the resistance lower.

B. Specific resistance.

R= p * L/A. Ohm*m.

P: (material constant)

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12
Q

What is electric conductance (G) and what is the SI unit?

A

The reciprocal of electric resistance:

G = 1/R. Siemenes.

G = I/U. (In Ohm’s Law).

G = A * conductivity (sigma) / length

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13
Q

What is specific conductance (sigma)?

What is the SI unit?

A

The reciprocal of resistivity:

Sigma = 1/p

P= materials constant.

SI unit: S/m.

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14
Q

How do you calculate the total resistance when connecting resistors in:

A. series?
B. Parallel?

A

A. R= R1 + R2 + R3.

B. R 1/R1 + 1/R2 + 1/R3.

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15
Q

What is Joule heating (W)?

What is the formula and SI unit?

A

The work done by the electric field when moving electric charge carriers that turns into another form of energy:

In Ohmic resistors: thermal energy.

W= R* I(2) * t or

W = U(2)/R * t.

Joule.

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16
Q

What is electric power (P el)?

A

The electric work done in unit of time:

P = U * I Watt.

17
Q

What does Kirchhoff’s two circuit laws explain?

A

They are the laws regarding the distribution of electric current and voltage in electrical circuits.

18
Q

What is Kirchhoff’s current law/junction law?

A

The currents flowing into a junction are equal to the currents flowing out of that junction - in a branched (parallelly connected) circuit, current is partitioned between the branches.

This is due to the conservation of energy.

19
Q

What is Kirchhoff’s voltage law/loop law?

A

The directed sum of voltages of electrical components along a loop within an electrical circuit is zero - within a loop (serially-connected circuit), voltage is partitioned between the electric components (resistances, capacitors etc).

20
Q

What is a RC circuit, and how do you compare an RC circuit and an LC circuit?

A

RC circuit is an electrical circuit consisting of an ohmic resistor and a capacitor.

An LC circuit consists of a coil and a capacitor.

21
Q

What is true for the total capatitance of a circuit?

A

The total capacitance is always smaller than any of the individual capacitances.

22
Q

What is the formula for charging?

A

Uc = Ub * (1-e -t/t)

23
Q

What is the formula for peak value of voltage and the effective value of voltage?

A

Peak value = amplitude (in a sine function).

Effective value of the voltage =

Ueff = Umax/sqare root of 2

Basic Physics (13 decks)

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