Radiologic Physics: Circuits, Electromagnetism, and X-Ray Equipment

Comprehensive question-and-answer flashcards based on lecture notes covering electrical units, Ohm's law, circuit components, electromagnetic induction, transformers, and x-ray generator concepts.

An x-ray tube is an example of current flow in what medium?

A vacuum (where electrons jump the gap between oppositely charged electrodes).

Which device increases or decreases voltage by a fixed amount through electromagnetic induction?

A transformer

What is Coulomb's law?

Electrostatic force between charges is directly proportional to the product of quantities and inversely proportional to the square of the distance between them.

What is the primary function of a rheostat?

To vary resistance (it is an adjustable or variable form of resistor).

How do electrons move in a metallic conductor?

Electrons are free to drift along the external surface.

Nearly all discussion of electricity deals with the movement of what type of charges?

Negative charges (electrons)

Which conductor dimension or condition provides the least electrical resistance?

A large cross-sectional area

What potential difference will maintain a current of $1\,\text{A}$ in a circuit with a resistance of $1\,\Omega$?

Volt ($\text{V}$)

What type of electrification occurs when electrons are removed from an object by rubbing it with another?

Electrification by friction

Which component converts AC to DC and allows electrons to flow in only one direction?

A diode (rectifier)

What is the unit of measure for electric current?

Ampere ($\text{A}$)

What is magnetic flux?

Curved lines of force in space

What is the magnetic classification of materials that are weakly attracted to magnets?

Paramagnetic

What is the unit of measure for electric potential, potential difference, or electromotive force (EMF)?

Volt ($\text{V}$)

How many volts are required to cause a current of $40\,\text{A}$ in a circuit having a resistance of $5\,\Omega$?

$200\,\text{V}$ (calculated using $V = IR = 40 \times 5 = 200\,\text{V}$)

In a series circuit, how is total resistance determined?

The total resistance is the sum of the individual resistances.

In the provided electrical schematic diagram, which symbol represents a transformer?

Symbol D

In the provided sine wave graph of a $60\,\text{Hz}$ current, how much time elapses between points A and E?

$1/60\,\text{s}$ (or $16.7\,\text{ms}$)

What is the distinct difference between direct current (DC) and alternating current (AC)?

DC electron flow is in one direction.

An x-ray imaging system has a $30\,\text{kW}$ generator. If the maximum tube voltage is $150\,\text{kV}$, what is the available tube current?

$200\,\text{mA}$ (calculated using $P = IV \implies I = \frac{30\,\text{kW}}{150\,\text{kV}} = 0.2\,\text{A} = 200\,\text{mA}$)

Given a closed loop of wire with no electron flow, under what condition can an electric current be induced?

When a changing (moving) magnetic field is present.

How is electrical energy produced in an electric generator?

A coil of wire is rotated in a magnetic field.

On what type of current does a transformer operate?

It operates on AC but not on DC.

How does the output current compare to the input current in a step-up transformer?

The output current is lower than the input current ($I_s = \frac{V_p I_p}{V_s}$).

Why do transformers have iron cores?

To intensify the magnetic field.

A transformer with a turns ratio of $1000:1$ is categorized as what type of transformer?

A step-down transformer (since secondary windings are fewer than primary windings).

What is the purpose of the autotransformer in an x-ray imaging system?

To supply a precise voltage to the filament circuit and high-voltage circuit of the x-ray imaging system.

What is the primary function of line compensation in an x-ray system?

It stabilizes incoming voltage.

What type of transformer is the filament transformer usually?

A step-down transformer

A filament transformer has $800$ primary windings and is supplied with $200\,\text{mA}$. If the secondary coil has $100$ windings, what will be the secondary current?

$1600\,\text{mA}$ (calculated using $I_s = \frac{I_p N_p}{N_s} = \frac{200 \times 800}{100} = 1600\,\text{mA}$)

Where is the exposure time control located in the x-ray circuit?

On the primary side of the high-voltage transformer.

What component does an automatic exposure control (AEC) device utilize for radiation measurement?

An ionization chamber located between the patient and the image receptor.

Which parameter is higher for a single-phase high-voltage generator than for a three-phase high-voltage generator?

Voltage ripple (which reduces x-ray quality).

What is the main advantage of full-wave rectification over half-wave rectification?

Higher energy x-rays

What is the unit of electrical power?

Watt ($\text{W}$)

What is the unit of electrical resistance?

Ohm ($\Omega$)