HamSandwich

Ham radio: the hobby that requires homework.

Study › Technician › T5C

T5C

ELECTRICAL PRINCIPLES

Capacitance and inductance terminology and units; Radio frequency definition and units; Impedance definition and units; Calculating power

Drill results are kept in this browser. Log in to keep them on your account and get a study plan.

T5C011 of 12

What describes the ability to store energy in an electric field?

Why A capacitor stores energy in the electric field between two conductive plates separated by an insulator, and capacitance is the measure of how much charge it holds per volt applied. The unit is the farad (F), though practical values are usually microfarads or picofarads. The companion property, inductance, stores energy in a magnetic field instead.
Watch out Inductance is the tempting opposite: it also stores energy, but in a magnetic field created by current flowing through a coil, not in an electric field between plates.
Capacitor = electriC field; inductor = magnetic field. Match the C's.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
T5C022 of 12

What is the unit of capacitance?

Why Capacitance is the ability of a component to store energy in an electric field, and it is measured in farads, named for Michael Faraday. One farad means one coulomb of charge stored per volt applied, which is a huge amount, so practical parts are rated in microfarads (uF) or picofarads (pF).
Watch out The henry is the unit of inductance, the ohm measures resistance or impedance, and the volt measures electrical potential difference.
Capacitor = Farad (Faraday), Inductor = Henry (Joseph Henry). Match the C and the L to their inventors.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
T5C033 of 12

What describes the ability to store energy in a magnetic field?

Why Inductance is the property of a coil or any conductor that lets it store energy in a magnetic field created by current flowing through it. It is measured in henries (H), with practical radio values often in microhenries or millihenries. An inductor opposes changes in current because the collapsing or building magnetic field induces a counter voltage.
Watch out Capacitance is the tempting opposite: it stores energy too, but in an electric field between plates, and it is measured in farads. Resistance dissipates energy as heat rather than storing it.
Magnetic field = coil = inductance (henries); electric field = plates = capacitance (farads).
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
T5C044 of 12

What is the unit of inductance?

Why Inductance is the property of a coil that opposes changes in current by storing energy in a magnetic field, and it is measured in henrys, abbreviated H. One henry means a current changing at 1 amp per second induces 1 volt across the coil. Practical radio inductors are usually in the microhenry (uH) or millihenry (mH) range.
Watch out The farad is the unit of capacitance, the electrical opposite of inductance, and is the most common mix-up; the coulomb measures quantity of charge and the ohm measures resistance or impedance.
Inductance = Henry (H), like the coil in a Ford's ignition; capacitance = Farad (F).
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
T5C055 of 12

What is the unit of impedance?

Why Impedance is the total opposition a circuit presents to alternating current, combining resistance with the reactance of capacitors and inductors. Because it is a form of opposition to current flow, it is measured in the same unit as resistance, the ohm, and gets the same symbol (the Greek capital omega). In Ohm's law form, impedance Z equals voltage divided by current.
Watch out The volt is the unit of electrical potential and the ampere is the unit of current; those are the quantities you divide to get impedance, not impedance itself. The coulomb measures quantity of electric charge.
Anything that opposes current, resistance, reactance or impedance, is measured in ohms.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
T5C066 of 12

What is the abbreviation for kilohertz?

Why Frequency units follow SI capitalization rules. The prefix kilo is always a lowercase k (uppercase K is reserved for kelvin), and hertz is abbreviated Hz with a capital H because it honors Heinrich Hertz, while the second letter of a unit symbol stays lowercase. Putting those together gives kHz.
Watch out KHz looks natural because sentences often start with a capital, but an uppercase K means kelvin in SI; all-lowercase khz misses that unit names taken from a person get a capital first letter.
Small k for kilo, big H for Hertz the man: kHz.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
T5C077 of 12

What is the abbreviation for megahertz?

Why SI symbols follow strict capitalization: the prefix mega is a capital M (lowercase m means milli, one thousandth), and the unit hertz is written Hz with a capital H because it honors Heinrich Hertz, followed by a lowercase z. Putting those together gives MHz, meaning one million cycles per second.
Watch out The version with a lowercase m would read millihertz, one thousandth of a hertz, which is a vastly different quantity, and the forms with a lowercase h or capital Z are simply not valid SI notation.
Big M for million, capital H for Hertz the man: MHz.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
T5C088 of 12

What formula is used to calculate electrical power (P) in a DC circuit?

Why Power is the rate of energy transfer, and in a DC circuit it equals the current through the device multiplied by the voltage across it: P = I x E, giving watts when I is in amperes and E is in volts. This is the basic power law that pairs with Ohm's law (E = I x R). Substituting Ohm's law gives the useful variants P = I squared x R and P = E squared / R.
Watch out The choices that divide voltage by current or current by voltage are mixing up power with resistance or conductance: E / I is actually Ohm's law solved for resistance, not power. The current-squared form only works when multiplied by resistance, not voltage.
Watts = Volts x Amps. Think "PIE": P = I x E.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
T5C099 of 12

How much power is delivered by a voltage of 13.8 volts DC and a current of 10 amperes?

Why Power in a DC circuit is the product of voltage and current, P = E x I. Here 13.8 volts times 10 amperes gives 138 watts. This is the basic power formula from the Ohm's law family, and it's worth memorizing alongside P = I squared x R and P = E squared / R.
Watch out The 23.8 watt choice comes from adding the two numbers and 3.8 from subtracting them; power is a product, not a sum or difference. The 0.7 watt figure is roughly a division of the two, which would give resistance-like or current-like results, not watts.
Volts times amps equals watts. 13.8 V at 10 A is the classic ham power supply: 138 W.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
T5C1010 of 12

How much power is delivered by a voltage of 12 volts DC and a current of 2.5 amperes?

Why DC power is simply voltage times current: P = E x I. With 12 volts across the load and 2.5 amperes flowing, P = 12 x 2.5 = 30 watts. This is the basic form of the power equation, the same one that gives P = I squared times R or P = E squared divided by R when you substitute Ohm's law.
Watch out The 4.8 watt choice comes from dividing 12 by 2.5, and 0.208 comes from dividing 2.5 by 12; power uses multiplication, not division. The 14.5 figure is just the two numbers added, which has no physical meaning.
PIE: P = I x E. Multiply volts by amps, never divide.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
T5C1111 of 12

How much current is required to deliver 120 watts at a voltage of 12 volts DC?

Why Power in a DC circuit is P = I x E, so current is found by dividing power by voltage: I = P / E. Here 120 watts divided by 12 volts gives 10 amperes. This is one of the three forms of the power wheel, alongside P = I x E and E = P / I.
Watch out The 0.1 ampere choice comes from flipping the division and computing 12 / 120, and 132 comes from simply adding the two numbers, which has no physical meaning.
PIE: P = I x E. Cover the unknown - current equals watts over volts, 120/12 = 10.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
T5C1212 of 12

What is impedance?

Why Impedance, symbol Z, measured in ohms, is the total opposition a circuit presents to alternating current. It combines resistance (opposition that dissipates power) with reactance from capacitors and inductors (opposition that depends on frequency), so Z is the AC counterpart of plain DC resistance.
Watch out The inverse of resistance is conductance, measured in siemens, and the inverse of reactance is susceptance; neither describes impedance, which is a sum of resistance and reactance effects, not an inverse.
Z = ohms of opposition to AC. Resistance + reactance = impedance.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
Baofeng BF-F8HP Pro Dual Band HandheldSponsored · View on Amazon →RG-213 Coax Cable 75ft with PL259 ConnectorsSponsored · View on Amazon →
← T5B All groups T5D →