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M3 > 3.6 DC Circuits > Flashcards

3.6 DC Circuits Flashcards

1
Q
A
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2
Q

What does Ohm’s law describe?

A

The relationship between current and voltage for most conductors

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3
Q

Who established Ohm’s law and when?

A

Georg Simon Ohm in 1827

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4
Q

What is the formula for Ohm’s law?

A

V = I * R

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5
Q

What do the symbols V, I, and R represent in Ohm’s law?

A
  • V: voltage in volts (V)
  • I: current in amperes (A)
  • R: resistance in ohms (Ω)
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6
Q

What is resistance?

A

The quotient of voltage to current, measured in ohms (Ω)

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7
Q

What is the characteristic of materials obeying Ohm’s law regarding resistance?

A

Resistance does not change over enormous ranges of voltage and current at constant temperature

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8
Q

What is Kirchhoff’s 1st Law?

A

At any junction in an electrical circuit, the sum of currents flowing towards that point equals the sum of currents flowing away from it

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9
Q

What can Kirchhoff’s 1st Law be used to calculate?

A

Unknown currents at a branching point in an electrical circuit

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10
Q

What is Kirchhoff’s 2nd Law?

A

The algebraic sum of all voltages around any closed loop is zero

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11
Q

What does Kirchhoff’s Voltage Law imply about voltage in a circuit?

A

Voltage is dropped through components with none left over in a closed loop

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12
Q

True or False: Voltage exists at a single point in a circuit.

A

False

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13
Q

What year were Kirchhoff’s circuit laws first described?

A

1845

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14
Q

Who first described Kirchhoff’s circuit laws?

A

Gustav Kirchhoff

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15
Q

What is the significance of Kirchhoff’s laws?

A

They are essential tools for the analysis of electric circuits

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16
Q

What is Ohm’s Law used for?

A

To calculate an unknown value for either voltage, current, or resistance

Ohm’s Law is expressed as V = IR, where V is voltage, I is current, and R is resistance.

17
Q

What does Kirchhoff’s 1st Law state?

A

The total current flowing towards a node is equal to the total current flowing away from the node

This is also known as Kirchhoff’s Current Law.

18
Q

What is the principle behind Kirchhoff’s 2nd Law?

A

The total EMF must equal the total PD in a circuit

EMF stands for electromotive force and PD stands for potential difference.

19
Q

How can unknown PD be calculated using Kirchhoff’s 2nd Law?

A

By subtracting the known PDs from the total EMF

This allows for the determination of unknown voltages in a circuit.

20
Q

In a parallel circuit, what is true about the PD across resistors?

A

The same PD is across all resistors connected in parallel

This is important for accurate calculations of current through each resistor.

21
Q

What is the voltage across the 6 Ω resistor in the example?

A

6 V

This voltage is the same as the voltage across the 12 Ω resistor due to their parallel connection.

22
Q

How do you calculate the current through a resistor using Ohm’s Law?

A

I = V/R

I is current, V is voltage, and R is resistance.

23
Q

What is the voltage across the 2 Ω resistor in the example?

A

3 V

This was calculated using Ohm’s Law after finding the current through the resistor.

24
Q

What is the total EMF calculated in the example?

A

9 V

This is derived from the sum of the PDs across the resistors connected in the circuit.

25
Q

Fill in the blank: According to Kirchhoff’s 1st Law, the total current at a node is equal to the total current _______.

A

flowing away from the node

26
Q

True or False: Kirchhoff’s 2nd Law can be used to find unknown voltages in a circuit.

A

True

27
Q

What does Internal Resistance (IR) refer to in a power supply?

A

A small resistor in series with the pure EMF of a power source

This resistance influences the terminal voltage depending on the current supplied.

28
Q

What is the terminal voltage of a power supply when it is off-load?

A

The terminal voltage is equal to the EMF

This occurs when no current flows through the internal resistance.

29
Q

What happens to the terminal voltage when the power supply is on-load?

A

The terminal voltage decreases compared to the EMF

This is due to the potential difference (PD) across the internal resistance.

30
Q

How is terminal voltage calculated when a power supply is on-load?

A

Terminal voltage = EMF - PD across internal resistance

The PD increases with higher current.

31
Q

What is the effect of a short-circuit on a power supply’s current?

A

A high current flows, limited only by the IR of the battery

This can lead to dangerously high short-circuit currents.

32
Q

What can excessive short-circuit current do to a power source?

A

It can quickly destroy the power source

Many power supplies have low IR, leading to high short-circuit currents.

33
Q

What factors contribute to achieving a stable terminal voltage in a power supply?

A

Choice and combination of power sources, voltage regulators, and load resistors

These components help maintain constant voltage and current.

34
Q

How is a battery’s Internal Resistance (IR) calculated?

A

IR = (Open-Circuit Voltage - Closed-Circuit Voltage) / Load Current

IR increases as the battery discharges.

35
Q

What is the typical IR of an AA battery cell?

A

About 0.1 Ω

This value affects the voltage between the terminals depending on the current.

36
Q

What is the danger associated with larger power sources compared to smaller ones?

A

Larger power sources can be potentially fatal

For example, a 20 V and 200 A source is much more dangerous than a small dry cell.

37
Q

What should users be cautious about regarding the ratings on batteries?

A

The terminal voltage and maximum current ratings

These ratings help prevent mishandling and dangerous situations.

38
Q

True or False: The terminal voltage of a power supply is always the same as its EMF.

A

False

The terminal voltage can be lower than the EMF when on-load.

39
Q

Fill in the blank: The actual voltage across the terminals of a power supply is called the _______.

A

terminal voltage

It varies based on the current supplied to an external load.

M3 (19 decks)

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