Correct answer: a semiconductor

Silicon is a material whose electrical conductivity lies between that of a conductor and an insulator.

Its conductivity can be controlled by:

• temperature
• doping with impurities

This makes it suitable for use in electronic components such as:

• diodes

• transistors

• integrated circuits

• It is not a good conductor like copper.

• It is not an insulator.

• It is not a superconductor.

Therefore, silicon is a semiconductor.

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Correct answer: C — semiconductor

A semiconductor is a material whose electrical conductivity falls between that of a conductor (such as copper) and an insulator (such as glass). Common semiconductor materials include silicon and germanium. Their conductivity can be precisely controlled by adding impurities (a process called doping) or by applying heat, light, or voltage — making them the foundation of modern electronics such as diodes and transistors.

• A. P-type conductor — P-type material is a doped semiconductor with an excess of positive "holes"; it is a specific type of semiconductor, not the general term for the in-between category.
• B. Intrinsic conductor — An intrinsic semiconductor is a pure, undoped semiconductor. While technically accurate as a sub-category, it does not describe the broad class of materials between insulators and conductors.
• D. N-type conductor — N-type material is a doped semiconductor with an excess of free electrons; again, a specific sub-type rather than the defining term.

Therefore, the correct general term for a material that falls between an insulator and a conductor is a semiconductor.

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Correct answer: the electrons orbit the nucleus

An atom consists of:

• a central nucleus containing protons and neutrons
• electrons surrounding the nucleus

The electrons move in regions (orbitals) around the nucleus.

• Protons and neutrons remain in the nucleus.
• They do not orbit each other.

Therefore, in an atom, the electrons orbit the nucleus.

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Correct answer: A — a positive ion

Atoms are electrically neutral because they contain equal numbers of protons (positive charge) and electrons (negative charge). When an atom loses an electron, it has one more proton than it has electrons, giving it a net positive charge. This charged atom is called a positive ion (or cation).

• B. an isotope — Isotopes differ in the number of neutrons in the nucleus, not in electron count. Losing an electron does not create an isotope.
• C. a negative ion — A negative ion (anion) is formed when an atom gains an extra electron, giving it a net negative charge — the opposite of this scenario.
• D. a radioactive atom — Radioactivity involves instability of the nucleus (e.g. excess neutrons or protons). Simply losing an electron does not make an atom radioactive.

Therefore, an atom that loses an electron has more protons than electrons and becomes a positively charged ion.

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Correct answer: a magnetic field

When an electric current flows through a conductor, it produces a magnetic field around the wire.

This is described by electromagnetic principles (e.g. Ampère’s Law).

• The magnetic field forms concentric circles around the conductor.

• Its strength depends on the current.

• An electric field exists due to voltage, not current flow alone.

• Electrostatic fields relate to stationary charges.

Therefore, the current produces a magnetic field.

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Correct answer: B — like

Magnetism follows the same fundamental rule as electric charges: like poles repel, unlike poles attract. A north pole placed near another north pole, or a south pole near another south pole, will experience a repulsive force pushing them apart.

• A. unlike — Unlike poles (north and south) attract each other, not repel.
• C. positive — "Positive" is not a valid term for magnetic poles; magnets have north and south poles, not positive and negative.
• D. negative — Similarly, "negative" does not describe a magnetic pole; this is an electrical term misapplied here.

Therefore, it is like magnetic poles (north–north or south–south) that repel one another.

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Correct answer: A computer speaker

A loudspeaker uses a permanent magnet and a voice coil to convert electrical signals into sound.

When current flows through the voice coil:

• it creates a magnetic field

• interacts with the permanent magnet

• causes movement of the speaker cone → produces sound

• Optical mice and keyboards do not rely on magnets.

• Magnetic loop antennas use currents and fields but not permanent magnets in this way.

Therefore, a common use for a magnet is in a computer speaker.

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Correct answer: A — copper

Copper is one of the best electrical conductors available, with a resistivity of approximately 1.68 × 10⁻⁸ Ω·m. This low resistivity means electrons flow through copper with very little opposition, making it the standard material for wiring, PCB tracks, and antenna elements in amateur radio.

• Carbon is a poor conductor with much higher resistivity; it is commonly used as a resistive material rather than a conductor.
• Silicon is a semiconductor, not a good conductor — its conductivity lies between that of conductors and insulators, which is why it is used in transistors and diodes.
• Aluminium is a reasonably good conductor but has a resistivity roughly 1.6 times higher than copper (~2.65 × 10⁻⁸ Ω·m), making it inferior to copper for most electrical applications.

Therefore, copper is the best conductor among the options listed and is the preferred material wherever low electrical resistance is required.

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Correct answer: resistance

Resistance is the property of a material that opposes the flow of electric current (electron flow).

It is measured in ohms (\(\Omega\)) and is defined by Ohm’s Law:

\[ R = \frac{V}{I} \]

• Current is the flow of electrons.
• Voltage is the potential difference driving the current.
• Power is the rate of energy transfer.

Therefore, the term is resistance.

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Correct answer: B — a conductor

A conductor is a material that has many free electrons in its atomic structure, allowing electric current (the flow of electrons) to pass through it with very little opposition. Metals such as copper, aluminium, and silver are typical conductors used in electrical and electronic circuits.

• A. an insulator — An insulator has very few free electrons and strongly resists the flow of current. Materials such as rubber, glass, and plastic are insulators used to prevent unwanted current flow.
• C. a resistor — A resistor is a component specifically designed to oppose and limit current flow, not to allow it freely.
• D. a dielectric — A dielectric is an insulating material used between the plates of a capacitor to store electric charge; it does not readily allow current to flow.

Therefore, of the options given, a conductor most readily allows electric current to flow due to its abundance of free electrons.

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Correct answer: A — an insulator

The plastic (or PVC) coating around wire is an electrical insulator. Insulating materials have very high resistance and do not allow electric current to flow through them easily. The coating serves two purposes: it prevents accidental contact between adjacent conductors, and it protects the wire from physical damage and moisture.

• B. a conductor — Conductors allow current to flow freely; plastic does the opposite, blocking current flow.
• C. an inductor — An inductor is a component (typically a coil of wire) that stores energy in a magnetic field; plastic coating has no such property.
• D. a magnet — A magnet produces a magnetic field; plastic coating is not magnetic and has no magnetic properties.

Therefore, the plastic coating on wire is an insulator, preventing unwanted current flow and keeping conductors safely separated.

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Correct answer: D — lead acid battery

A lead acid battery is an electrochemical device that converts stored chemical energy into electrical energy. Through a reversible chemical reaction between lead plates and sulphuric acid electrolyte, it generates and maintains an electromotive force (EMF), making it a true source of electrical energy.

• A. p-channel FET — A field-effect transistor is an active semiconductor device used to switch or amplify signals; it consumes electrical energy rather than generating it.
• B. carbon resistor — A resistor is a passive component that dissipates electrical energy as heat; it cannot generate or store energy.
• C. germanium diode — A diode is a semiconductor device that controls the direction of current flow; it is not a source of electrical energy.

Therefore, of the options given, only the lead acid battery is a source of electrical energy, producing an EMF from an internal chemical reaction.

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Correct answer: can be re-charged

A lead-acid battery is a secondary (rechargeable) battery, meaning it can be recharged after use.

A typical torch battery (e.g., zinc-carbon or alkaline) is:

• a primary battery

• not designed to be recharged

• Both types have two terminals.

• Both contain electrolytes.

• Both can be discharged.

Therefore, the key difference is that only the lead-acid battery can be re-charged.

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Correct answer: A — increases

In metallic conductors, resistance rises with temperature. As the metal heats up, the atoms in the crystal lattice vibrate more vigorously. These increased vibrations cause more frequent collisions with the free electrons that carry current, impeding their flow and raising the overall resistance. This property is described by the temperature coefficient of resistance (α), which is positive for metals.

• B — decreases: This applies to semiconductors and thermistors (NTC type), not metallic conductors. Metals behave the opposite way.
• C — remains constant: Resistance is temperature-dependent in metals; only specialised alloys (e.g. Manganin, Constantan) approach near-constant resistance, and even these are not perfectly constant.
• D — becomes negative: Resistance is a physical quantity that cannot become negative. Negative temperature coefficients exist, but they describe a rate of change, not a negative resistance value.

Therefore, as temperature increases in a metallic conductor, the increased lattice vibration impedes electron flow and resistance increases.

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Correct answer: electrons

In an n-type semiconductor, impurities are added that provide extra electrons to the crystal structure.

These free electrons are able to move through the material and act as the majority charge carriers responsible for current flow.

• Holes are the majority carriers in p-type material.
• Positive ions are fixed in the lattice and do not move.
• Photons are not charge carriers.

Therefore, the current carriers in an n-type semiconductor are electrons.

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Correct answer: holes

In a p-type semiconductor, impurities are added that create a deficiency of electrons in the crystal structure.

These missing electrons are called holes, which behave as positive charge carriers and move through the material as nearby electrons fill the gaps.

• Photons are not charge carriers.
• Electrons are the majority carriers in n-type material.
• Positive ions are fixed in the crystal lattice and do not move.

Therefore, the current carriers in a p-type semiconductor are holes.

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Correct answer: B — does not let electricity flow through it

An electrical insulator is a material that resists the flow of electric current. Its atoms hold their electrons tightly, leaving very few free charge carriers available to support current flow. Common insulators include rubber, glass, plastic, and dry wood.

• A is incorrect — a material that allows current in one direction only is a diode (a semiconductor device), not an insulator.
• C is incorrect — a material that conducts when light shines on it is a photoconductor or light-dependent resistor (LDR), which is a semiconductor property.
• D is incorrect — a material that lets electricity flow through it is a conductor, such as copper or aluminium.

Therefore, an insulator is defined by its property of not allowing electric current to pass through it.

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Correct answer: D — glass, air, plastic, porcelain

Electrical insulators are materials that resist the flow of electric current because their electrons are tightly bound and not free to move. Good insulators are essential in amateur radio construction for standoff insulators, antenna end supports, coax connectors, and feed-through fittings. Glass, air, plastic, and porcelain are all classic insulators with very high resistivity.

• A. plastic, rubber, wood, carbon — Carbon is a conductor (used in resistors and electrodes), so this group is disqualified.
• B. glass, wood, copper, porcelain — Copper is one of the best electrical conductors known, so this group is disqualified.
• C. paper, glass, air, aluminium — Aluminium is a metal conductor widely used in antenna elements and feedlines, so this group is disqualified.

Therefore, the only group consisting entirely of good electrical insulators is glass, air, plastic, and porcelain.

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Correct answer: C — gold, silver, aluminium

Electrical conductors are materials that allow electric current to flow freely because they have many loosely bound (free) electrons. Metals are the most common good conductors. Gold, silver, and aluminium are all metals and are well-known conductors used widely in electronics and electrical engineering. Silver has the highest conductivity of all metals, gold resists corrosion and is used in connectors, and aluminium is widely used in power transmission lines.

• A. copper, gold, mica — Copper and gold are excellent conductors, but mica is an electrical insulator, commonly used as a dielectric in capacitors precisely because it does not conduct.
• B. gold, silver, wood — Gold and silver are good conductors, but wood is a poor conductor (effectively an insulator in dry conditions) and does not belong in this group.
• D. copper, aluminium, paper — Copper and aluminium are good conductors, but paper is an insulator and is sometimes used as a dielectric material in capacitors.

Therefore, the only group consisting entirely of good electrical conductors is gold, silver, and aluminium.

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Correct answer: D — current

Electric current is defined as the flow (movement) of electrons through a conductor. In a circuit, when a potential difference (voltage) is applied, electrons move from the negative terminal toward the positive terminal — this movement is what we call current, measured in amperes (A).

• A. Voltage — Voltage is the driving force (electromotive force or potential difference) that pushes electrons around a circuit, not the flow itself.
• B. Resistance — Resistance is the opposition to the flow of electrons, measured in ohms (Ω).
• C. Capacitance — Capacitance is the ability of a component to store electric charge, measured in farads (F).

Therefore, the correct term for the flow of electrons in an electric circuit is current.

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