Circuit Components and Symbols Lesson Test

Answer: C

Correct answer: The positive terminal. In a cell symbol the longer line is the positive terminal and the shorter line is the negative terminal. A handy memory aid is to picture the long line as a plus sign with a tall vertical stroke.

• A: Ground has its own symbols, such as stacked lines of shrinking length; a cell plate is a source terminal.
• B: Internal resistance is not drawn as a plate; the two lines only mark the two terminals of the cell.
• C (correct): The longer plate of a cell symbol marks the positive side, where conventional current leaves the source.
• D: This reverses the convention; the short, often thicker plate is the negative side.

Answer: D

Correct answer: The cathode. The triangle points in the direction conventional current flows easily, from anode to cathode. The bar at the tip of the triangle is the cathode, and the band on a physical diode marks the same end.

• A: A gate is a terminal of a field-effect transistor, not of a two-lead diode.
• B: The anode is the flat side of the triangle, the end current enters when the diode conducts.
• C: An emitter belongs to a bipolar transistor and is marked by an arrow on a three-terminal symbol.
• D (correct): The bar across the triangle's point marks the cathode, matching the painted band on a real diode.

Answer: C

Correct answer: The resistance can be adjusted. A diagonal arrow drawn through a resistor symbol means its resistance can be changed, making it a variable resistor. An arrow pointing at the side of the body instead shows a potentiometer's wiper.

• A: Light-emission arrows belong to the LED symbol, not to resistors.
• B: Ground has its own symbols, such as stacked lines or a triangle.
• C (correct): An arrow through the body marks a variable resistor, such as a rheostat.
• D: One-way flow is shown by a diode's triangle and bar, not by an arrow through a resistor.

Answer: D

Correct answer: A lamp. Several symbols are circles, so the mark inside decides the meaning. An X inside the circle identifies a lamp, a load that turns electrical energy into light and heat.

• A: A motor is drawn as a circle containing the letter M.
• B: A voltmeter is a circle containing the letter V, not an X.
• C: An AC source is a circle containing a sine-wave squiggle.
• D (correct): A circle with an X inside, or with a small filament loop, is the usual symbol for a lamp.

Answer: A

Correct answer: The wires pass each other without connecting. Because the page is flat, wires often have to cross. In the common convention, a crossing without a dot means the conductors do not touch, while a dot marks an intended junction.

• A (correct): Under the usual convention only a dot marks a junction, so a plain crossing is like a highway overpass.
• B: Joining is shown with a solid dot; treating every intersection as a node is a classic misreading.
• C: A switch is always drawn with its own blade and contact symbol; a crossing adds no part.
• D: A short needs a real low-resistance connection, and a plain crossing is not a connection at all.

Answer: C

Correct answer: The current through the switch is zero. In electrical terms, open means the contacts are apart and the circuit is broken, so the current through that branch is zero. Closed means the contacts touch and the switch acts like a short piece of wire.

• A: An open switch adds a gap, not a low-resistance path, so current cannot rise through it.
• B: This borrows the water-valve meaning; in electricity an open switch breaks the path.
• C (correct): An open switch has its contacts apart, so it breaks the loop and no current can pass through it.
• D: Switch state is mechanical contact, not temperature; open simply means the contacts do not touch.

Answer: B

Correct answer: A photodiode, a light sensor. Light arrows tell the direction light travels. Outward arrows mean the part emits light (an LED); inward arrows mean the part receives light, as a photodiode does.

• A: A Zener diode is marked by bent tips on its bar, not by light arrows.
• B (correct): Arrows pointing toward the diode show light arriving, which marks a light detector such as a photodiode.
• C: A Schottky diode is marked by S-shaped hooks on its bar, not by arrows.
• D: An LED uses arrows pointing outward, away from the diode, to show light leaving it.

Answer: D

Correct answer: A motor. Circle symbols are identified by what is inside them. M stands for motor, a load that receives electrical energy and produces mechanical rotation, as with the fan here.

• A: A lamp is a circle with an X or a small filament loop.
• B: A current meter is a circle with A, for ammeter.
• C: A generator is a circle with G and feeds energy into the circuit rather than drawing it.
• D (correct): A circle with M is a motor, a load that turns electrical energy into rotation.

Answer: B

Correct answer: A transistor. Reference letters follow drafting conventions: R for resistors, C for capacitors, L for inductors, F for fuses and Q for transistors. So Q3 is the third transistor in the drawing.

• A: Capacitors use the letter C.
• B (correct): By common convention, Q is the reference letter for transistors.
• C: Fuses use the letter F.
• D: Inductors use the letter L.

Answer: B

Correct answer: Microfarads. Capacitance is measured in farads (F). A farad is very large, so practical values use prefixes such as microfarads (µF). The label means capacitor number two, rated 100 µF.

• A: The henry measures inductance, which belongs to coils labeled L.
• B (correct): The farad is the unit of capacitance, and µ is the micro prefix.
• C: The ohm measures resistance and is written with the Ω symbol.
• D: The coulomb measures charge, which is a capacitor's stored quantity, not its rating.

Answer: A

Correct answer: 100 nF. Micro means $10^{-6}$ and nano means $10^{-9}$, so 1 µF = 1,000 nF. Multiply:

nF.

• A (correct): One microfarad equals 1,000 nanofarads, so 0.1 µF times 1,000 is 100 nF.
• B: This divides by 10 instead of multiplying by 1,000 when converting microfarads to nanofarads.
• C: 1,000 nF equals 1 µF, which is ten times larger than the labeled value.
• D: This drops two decimal places; 1 nF is only 0.001 µF.

Answer: A

Correct answer: Six. A single pole with two throws needs three terminals: the common contact and one contact for each throw. A DPDT switch doubles that arrangement, so it has

terminals.

• A (correct): Each pole has a common contact plus two throw contacts, and two poles times three terminals gives six.
• B: Three terminals is an SPDT switch: one common contact plus two throws for a single pole.
• C: Four would give each pole only two connections, leaving out one of the throws on each pole.
• D: Two terminals describe a plain SPST on-off switch with a single pole and throw.

Answer: B

Correct answer: 4,700 Ω. In this marking the letter replaces the decimal point, so 4K7 means 4.7 kΩ. Since 1 kΩ = 1,000 Ω, the value is

• A: This ignores the k multiplier, which means times 1,000.
• B (correct): The K stands in for the decimal point and means kilo-ohms: 4.7 kΩ = 4,700 Ω.
• C: This drops the decimal point that the letter K replaces.
• D: This keeps the decimal but forgets that k multiplies by 1,000.

Answer: A

Correct answer: An iron-core step-down transformer. Two coils drawn facing each other with parallel lines between them, labeled T, are a transformer with an iron core. Because the secondary (output) has fewer turns than the primary, the transformer steps the voltage down.

• A (correct): Two coils sharing a core, labeled T, form a transformer, and fewer secondary turns lower the voltage.
• B: Separate inductors would carry L labels and would not share a core drawn between them.
• C: A relay is shown as a coil plus switch contacts labeled K or RY, not as two facing coils.
• D: A step-up transformer has more turns on the secondary than on the primary, which raises the voltage.

Answer: C

Correct answer: Remove power from the circuit before measuring. An ohmmeter works by sending its own test current through the part and reading the result. Any voltage already in the circuit spoils the reading and can damage the meter, so power must be removed first.

• A: Outside voltage is exactly what corrupts an ohmmeter reading and can damage the meter.
• B: Changing to an ammeter function measures current, not resistance, and does not answer the technician's question.
• C (correct): An ohmmeter supplies its own small test current, so the part must be de-energized for a valid, safe reading.
• D: Series placement is how an ammeter is used; an ohmmeter still needs the power off to read correctly.

Answer: A

Correct answer: The lamp goes dark and the battery current rises sharply. A closed switch behaves like a plain wire. Placed across the lamp it forms a short circuit: current takes the low-resistance path, the lamp goes dark, and the source current becomes very large, which is what fuses and breakers are meant to stop.

• A (correct): The closed switch shorts the lamp, starving it of current while the source pushes a large current through the shortcut.
• B: A closed switch acts like a wire, and a wire across a load is a short that changes the circuit a great deal.
• C: The switch offers a near-zero-resistance path, so current goes around the lamp rather than through it.
• D: Bypassing the lamp lowers the circuit resistance, which raises the battery current rather than stopping it.

Answer: B

Correct answer: R1 and R5 are connected, but their physical spacing is unknown. A schematic is like a subway map: it keeps connections correct but distorts distances. The line tells you the two resistors are electrically joined; it says nothing about how far apart they are on the board.

• A: Page order does not set timing; current in a loop flows everywhere at once.
• B (correct): A schematic shows what connects to what, not where parts sit or how long the traces are.
• C: An ideal conductor line has no resistance regardless of its drawn length.
• D: Drawing distance does not show physical distance; the two parts may sit side by side.

Answer: D

Correct answer: In series inside the heater branch. An ammeter measures the current that flows through it, so it must be inserted in series in the path being measured. To read only the heater's current, it goes inside the heater branch, after the junction where the branches split.

• A: This is how a voltmeter is connected; an ammeter there would create a near short around the heater.
• B: There it would read the total current of both branches, not the heater alone.
• C: An ammeter across a source acts as a short and can blow the meter's fuse or damage the source.
• D (correct): The branch is opened and the meter inserted so all of the heater's current passes through it.

Answer: D

Correct answer: The path opens, because the button is normally closed. Diagrams show switches in their normal, unpressed state. Contacts drawn touching mean a normally closed (NC) button, which opens the path while it is held down.

• A: The drawing shows the resting state; the real button still moves when pressed.
• B: A normally open button is drawn with its contacts apart, not touching.
• C: A pushbutton only makes or breaks its own contacts; it does not create a ground connection.
• D (correct): Switches are drawn at rest, so touching contacts mean an NC button that breaks the path while pressed.

Answer: C

Correct answer: 3.6 V. An unloaded potentiometer divides the supply in proportion to resistance measured from the reference end.

• A: This uses the 6 kΩ between the wiper and the top end, measuring from the wrong end.
• B: This is the midpoint voltage, which would apply only with the wiper halfway along the track.
• C (correct): 9 V × 4/10 = 3.6 V.
• D: This divides 9 V by 4 instead of taking the 4/10 fraction of the track.

Answer: A

Correct answer: 2,640 µC. Charge equals capacitance times voltage.

• A (correct): Q = CV = 220 µF × 12 V = 2,640 µC.
• B: This misplaces the decimal; 220 × 12 is 2,640, not 26.4.
• C: This divides capacitance by voltage instead of multiplying them.
• D: This adds the two numbers instead of multiplying them.

Answer: A

Correct answer: Both provide overcurrent interruption; many circuit breakers are resettable. Both devices sit in series with a circuit and open it when current exceeds a safe level, protecting the wiring from overheating. A fuse does this by melting a thin metal link, so it must be replaced with one of the same rating. A breaker uses a thermal or magnetic trip mechanism that opens contacts, which can then be closed again with the handle. Neither one is a meter or a source; they are protective switches.

• A (correct): The fuse is generally sacrificial while many breakers can be reset after correcting the issue.
• B: Protection devices interrupt faults rather than primarily display measurements.
• C: Those describe neither ordinary device.
• D: Neither creates its own source voltage.

Answer: D

Correct answer: 20 mA. The series resistor takes whatever voltage the LED does not: 9 V − 2 V = 7 V.

• A: This uses only the LED's 2 V instead of the voltage left for the resistor.
• B: This adds the LED drop to the supply voltage instead of subtracting it.
• C: This uses the full 9 V across the resistor and ignores the LED's 2 V drop.
• D (correct): The resistor takes 9 − 2 = 7 V, and 7 V ÷ 350 Ω = 0.02 A = 20 mA.

Answer: D

Correct answer: The plus-marked lead must go to the more positive point. A curved or filled plate with a plus sign marks a polarized capacitor, such as an electrolytic type. Its positive lead must stay more positive than the other; reversing it can make the part overheat, leak or burst.

• A: That is true of nonpolarized capacitors drawn with two straight plates, not of this one.
• B: Nothing in the symbol calls for a fuse, and capacitance values are not fuse ratings.
• C: Storing charge between the plates is exactly what a capacitor is for.
• D (correct): This marks a polarized capacitor, which can overheat, leak or burst if connected backward.

Answer: B

Correct answer: 4 V. Convert 20 mH to 0.020 H, then apply the inductor formula.

• A: This multiplies inductance by current change but ignores the time over which it happens.
• B (correct): V = LΔI/Δt = 0.020 × 3 ÷ 0.015 = 4 V.
• C: This uses 20 instead of 0.020 H, forgetting that m means milli.
• D: This divides the current change by the time but leaves out the inductance.

Answer: A

Correct answer: The common 0 V reference, usually the battery's negative side. Ground can mean earth, chassis or circuit reference. In a battery-powered device it is the common reference point for voltages, usually the negative terminal, and all ground marks on the drawing are one node.

• A (correct): In battery-powered gadgets, ground is the chosen reference node, normally the negative terminal.
• B: Every ground symbol in one schematic is the same node, even when drawn far apart.
• C: Earth ground is used for safety in building wiring; a handheld radio has no link to the earth.
• D: Ground is not a load and does not soak up current; it is a shared return and reference.

Answer: B

Correct answer: An inductor with an iron core. A row of smooth loops labeled L is an inductor. Parallel straight lines alongside the coil show an iron or steel core, which greatly increases the inductance. Only one coil is present, so it is not a transformer.

• A: A transformer needs two coils facing each other and a T label; here there is only one coil.
• B (correct): Smooth loops labeled L are an inductor, and straight lines beside the coil indicate an iron or steel core.
• C: A resistor is a sharp zigzag or a rectangle, not smooth loops, and it would carry an R label.
• D: A capacitor is two plates with a gap, and its label would begin with C.

Answer: A

Correct answer: The contact closes, so the small control current switches on the horn. Matching labels such as K1 mark the coil and contacts of one relay. When current flows in the coil, its magnetic field moves the contacts, closing a normally open contact, so a small control current can switch a large load.

• A (correct): K1 is a relay: the energized coil's magnetic field pulls the normally open contact shut.
• B: The coil and contact circuits are separate; only the magnetic pull links them.
• C: The coil operates the contacts; overcurrent protection is the job of a fuse or breaker.
• D: A normally open contact closes when the coil is energized; it would open only if it were normally closed.

Answer: A

Correct answer: A PNP transistor. On a bipolar transistor, the arrow sits on the emitter. If it points out of the symbol, the transistor is NPN; if it points in, it is PNP.

• A (correct): An emitter arrow pointing in identifies a PNP bipolar transistor.
• B: NPN emitter arrows point out of the symbol: not pointing in.
• C: A photodiode is a triangle and bar with arrows pointing in, and it has only two leads.
• D: Field-effect transistors are drawn with gate, drain and source rather than base, collector and emitter.

Answer: D

Correct answer: The lamp dims or goes dark because the meter blocks most of the current. A voltmeter belongs across the part being measured, in parallel. Its very high internal resistance means that if it is placed in series it blocks nearly all the current, so the lamp dims or goes dark.

• A: That is the danger of an ammeter in parallel; a voltmeter's resistance is very high, not low.
• B: The meter is in the wrong place; a voltmeter must be connected across the lamp.
• C: A meter does not supply energy; it only measures.
• D (correct): A voltmeter has very high internal resistance, so in series it nearly stops the loop current.

Answer: C

Correct answer: 9 V. Total resistance is

kΩ, so the current is 12 V ÷ 6 kΩ = 2 mA. The voltmeter across the 4.5 kΩ resistor reads 2 mA × 4.5 kΩ = 9 V.

• A: This is the voltage across the 1.5 kΩ resistor, not the 4.5 kΩ one.
• B: This splits the voltage equally, which would happen only if the resistors were equal.
• C (correct): The current is 12 V ÷ 6 kΩ = 2 mA, and 2 mA × 4.5 kΩ = 9 V.
• D: This is the whole battery voltage; the voltmeter is across only one of two series parts.

Answer: C

Correct answer: R4 is a 500 Ω resistor and F2 is a fuse rated 0.5 A. Rectangles can stand for resistors, fuses or other parts, so the label and unit decide. R4 with a value in ohms is a resistor. F2 with a current in amperes is a fuse, and 500 mA = 0.5 A.

• A: This ignores the F label and the ampere unit, which identify a fuse, not a resistor.
• B: A prefix does not make a part variable; a variable resistor is shown by an arrow through the body.
• C (correct): Ohms with an R label identify a resistor, and amperes with an F label identify a fuse; 500 mA equals 0.5 A.
• D: This swaps the letter codes; R marks a resistor and F marks a fuse, and fuses are rated in amperes.

Answer: D

Correct answer: A very large current flows that can blow the meter's fuse. An ideal ammeter has nearly zero resistance so that it does not disturb a loop when placed in series. Connected across a battery, that low resistance becomes a near short: a very large current flows and can blow the meter's fuse or damage the battery. It should be inserted in series with the lamp.

• A: With almost no resistance across a voltage source, the meter draws a very large current, not none.
• B: The lamp's current flows in the lamp's path; the meter there must be in series with the lamp.
• C: An ammeter measures current, not voltage, and this connection gives no useful reading.
• D (correct): An ammeter has nearly zero resistance, so across a source it acts as a short circuit.

Answer: B

Correct answer: It lights, because every ground symbol in a drawing is the same node. Every ground symbol in one schematic is the same node, even when drawn apart. Current leaves the battery's positive terminal on the +9 V rail, passes through the lamp to ground, and returns through ground to the negative terminal, so the loop is complete and the lamp lights.

• A: Ground is a reference node, not a load; current returns through it to the source.
• B (correct): Ground symbols share one reference node, so the loop is complete from +9 V through the lamp back to the battery.
• C: Ground symbols are connected by convention even when drawn far apart.
• D: In a battery circuit, ground is just the chosen 0 V reference, with no need for an earth connection.

Answer: C

Correct answer: −5 V. Voltage is always a difference between two points:

The negative sign shows that point A is at the lower potential.

• A: This is the size of the difference, but it uses B minus A instead of A minus B and loses the sign.
• B: This adds the two node voltages, but a voltmeter reports a difference between two points.
• C (correct): $V_{AB}=V_A-V_B=3-8=-5$ V, so A is 5 V lower than B.
• D: This adds the voltages and then applies a sign; the reading is a subtraction, not a sum.

Answer: C

Correct answer: Current through the series lamp branch drops to zero. In a series path, the same current must pass through every part, so one break anywhere stops current everywhere in that loop. An open fuse is such a break, just like an open switch. The battery voltage does not disappear; it now appears across the open fuse instead of across the lamp. Be careful not to stretch the conclusion further: an open fuse does not make the whole device safe, since other circuits or stored energy may remain.

• A: An open fuse creates a break, not a low-resistance bypass.
• B: An open branch stops current but does not remove the battery's voltage, which still appears across the gap.
• C (correct): The opened series fuse breaks the only path through that branch, regardless of the switch state.
• D: Other branches and stored energy may remain hazardous.

Answer: B

Correct answer: 4 µA. Capital M means mega, 10⁶, so 1.5 MΩ = 1,500,000 Ω.

• A: This ignores the prefix and divides 6 V by just 1.5 Ω.
• B (correct): 1.5 MΩ is 1,500,000 Ω, and 6 ÷ 1,500,000 = 0.000004 A = 4 µA.
• C: This treats capital M as kilo; 4 mA would flow through 1.5 kΩ.
• D: This treats the prefix as 10⁹ instead of mega, 10⁶.

Answer: D

Correct answer: 12 V, the full battery voltage. A blown fuse acts like an open switch, so the loop current drops to zero. With no current, the lamp has no voltage across it, and the battery's full 12 V appears across the gap in the fuse.

• A: Splitting the voltage evenly assumes current still flows through two equal loads, which is not the case.
• B: Zero current does not mean zero voltage; the source voltage still exists and appears across the gap.
• C: An ideal source gives a steady voltage; the reading across the gap settles at the battery voltage.
• D (correct): With no current, the lamp drops no voltage, so the whole 12 V appears across the open fuse.

Answer: B

Correct answer: 11.75 V. Convert both prefixes first: 4.7 kΩ = 4,700 Ω and 2.5 mA = 0.0025 A. Then apply Ohm's law:

• A: This converts kilohms to ohms but forgets to convert 2.5 mA to 0.0025 A.
• B (correct): Converting both prefixes gives 4,700 Ω × 0.0025 A = 11.75 V.
• C: This divides the resistance by the current instead of multiplying them as Ohm's law requires.
• D: This converts milliamperes to amperes but leaves the resistance as 4.7 Ω instead of 4,700 Ω.

Answer: C

Correct answer: The lamp lights, but the LED stays dark. Trace each branch. The fuse is intact and the switch is closed, so the lamp branch completes a loop and the lamp lights. In the other branch, the cathode bar faces the positive side, so the LED is reverse biased and its branch carries no current. Parallel branches work independently.

• A: The lamp branch has nothing blocking it, and the LED is the part facing the wrong way.
• B: The LED's bar faces the positive side, so it is reverse biased and does not conduct.
• C (correct): The lamp branch has a complete path, while the reversed LED is reverse biased and blocks its branch.
• D: The LED blocks only its own parallel branch; the lamp branch still completes the loop.

Answer: D

Correct answer: 5 mA. In a series loop the resistor takes whatever voltage the LED does not: 12 V − 3 V = 9 V. Convert 1.8 kΩ to 1,800 Ω.

• A: This divides the full 12 V by the resistance, forgetting that the LED takes 3 V of the supply.
• B: This uses 1.8 Ω instead of 1,800 Ω, ignoring the k prefix and giving a current a thousand times too large.
• C: This uses the LED's 3 V drop instead of the 9 V left across the resistor.
• D (correct): The resistor gets 12 V − 3 V = 9 V, and 9 V ÷ 1,800 Ω = 0.005 A, which is 5 mA.

Answer: A

Correct answer: A source that turns mechanical rotation into electrical energy. Motors and generators are both circles, labeled M and G. Decide by the direction of energy flow: this machine is driven mechanically and feeds the circuit, so it is a generator, an electrical source.

• A (correct): The wind drives the machine and it feeds the circuit, so it is a generator acting as a source.
• B: That describes a motor, which receives power to spin something; here the wind does the spinning.
• C: A current meter is a circle labeled A; G marks a generator.
• D: Ground uses line, rake or triangle symbols, not a circle labeled G.

Answer: A

Correct answer: A Zener diode, deliberately reverse-biased to hold a set reference voltage. A bar with bent tips, like a stretched Z, identifies a Zener diode. The triangle points from anode to cathode, so with the bar at the positive line the diode is reverse-biased. Zeners are designed to work this way, conducting in reverse at a set voltage to act as a reference.

• A (correct): The bent-tipped bar marks a Zener, which is designed to conduct in reverse at a set voltage, so placing its cathode toward positive is the intended use.
• B: An LED is marked by outward arrows, and with the cathode toward positive this diode is reverse-biased, not forward-biased.
• C: A Schottky bar has S-shaped hooks, and this diode's orientation puts it in reverse bias.
• D: The bent tips identify a special Zener variant, for which reverse connection is the normal working arrangement.

Answer: C

Correct answer: An earth ground, a real safety connection to the earth. Three horizontal lines that get shorter toward the bottom are the earth-ground symbol. Connecting an appliance's metal case to earth ground is a safety measure, giving fault current a path other than through a person.

• A: Chassis ground is usually drawn like a rake or comb; the stacked shrinking lines mark earth ground.
• B: A cell is two unequal lines of a different form, and nothing here supplies energy to the case.
• C (correct): The three lines shrinking toward the bottom are the earth-ground symbol, used for safety in building wiring.
• D: A signal or circuit ground is often drawn as a plain triangle and is just a voltage reference, not a safety path to the earth.

Answer: D

Correct answer: Both stay lit at normal brightness. Lamps connected across the same two wires are in parallel. Each branch gets the full 12 V and has its own current, so when one filament opens only that branch stops; the other two keep shining normally.

• A: Every lamp going dark is what happens in a series string; these lamps are in parallel.
• B: Each parallel branch still sees the same 12 V, so the remaining lamps keep the same current and brightness.
• C: Parallel branches each get the full battery voltage; voltage is not divided among them.
• D (correct): In parallel, each lamp has its own path across the battery, so opening one branch leaves the others working.

Answer: D

Correct answer: A capacitor. Two equal-length parallel plates represent a capacitor, which stores energy in an electric field and is rated in farads. Unequal plates would instead mean a battery cell.

• A: A cell's two lines are of unequal length, with the longer line marking the positive terminal.
• B: A resistor is drawn as a zigzag or a small rectangle.
• C: A fuse is usually a small rectangle or a wavy line between terminals, not two equal plates.
• D (correct): Two equal parallel plates separated by a gap is the standard capacitor symbol.

Answer: A

Correct answer: A light-emitting diode. The basic diode symbol plus outward arrows means a light-emitting diode: the arrows show light coming out. Inward arrows would mean light coming in, as in a photodiode.

• A (correct): Outward arrows show light leaving the device, which marks an LED.
• B: A photodiode senses light, and its symbol has arrows pointing inward toward the diode, not outward.
• C: A Zener diode is shown by bent tips on the bar, not by arrows.
• D: A lamp is drawn as a circle with an X inside, not as a diode symbol.

Answer: C

Correct answer: The fuse opens, because 0.3 A is more than its 0.25 A rating. Convert the rating first: 250 mA = 250 × 0.001 A = 0.25 A. A steady 0.3 A is above that rating, so the fuse is expected to melt and open the circuit, stopping current in that path.

• A: This compares the numbers without converting units; 250 mA is only 0.25 A.
• B: A fuse protects against excess current, melting when the current through it is too high.
• C (correct): Converting 250 mA gives 0.25 A, so 0.3 A is an overload and the fuse link should melt and open the path.
• D: Resetting describes a circuit breaker; a fuse is sacrificial and must be replaced after it opens.

Answer: B

Correct answer: The pin connects to the positive supply rail. Supply rails are often shown by labels instead of long wires. VCC means the point is connected to the positive supply, so every point marked VCC is the same node as the positive rail.

• A: A named rail label shows a connection; it is not a mark for an unused pin.
• B (correct): A rail label such as VCC means the point joins the positive supply, even when no wire is drawn to the battery.
• C: Ground is shown with ground symbols; VCC names the positive supply.
• D: Signal lines carry information and are named for their signal; VCC is a power label.

Answer: B

Correct answer: The red lamp goes out and the green lamp lights. An SPDT switch has one common contact that connects to either of two fixed contacts. Flipping it moves the connection from the red lamp's path to the green lamp's path, so the red lamp turns off and the green lamp turns on.

• A: An SPDT switch's common contact touches only one fixed contact at a time, so it never feeds both lamps together.
• B (correct): Flipping the switch moves the common contact from the red lamp's throw to the green lamp's throw, steering current to the other path.
• C: An SPDT switch steers current to one of two paths; turning everything off needs a center-off or different switch.
• D: Changing the switch position changes which fixed contact the common terminal touches, so the lit lamp changes.