PRELIMINARY STAGE 2024
CONTEST 16
Benkum SHS: 61 points (Winner)
Kadjebi-Asato SHS: 44 points
Assin Manso SHS: 40 points
Contest 17
St. Hubert Seminary SHS: 64 points (Winner)
Fafraha Community SHS: 38 points
Nandom SHS: 35 points
Contest 18
Our Lady of Grace SHS: 59 points (Winner)
Assin State College: 38 points
Bueman SHS: 17 points
ROUND 5 - RIDDLE
RIDDLE
I am a type of material.
I'm usually solid though liquid forms of me are known.
My electrical conductivity increases as temperature rises, the opposite of how a metal behaves.
Examples of me are gallium, arsenide, and germanium.
Who am I?
ANSWER: Semiconductors
EXPLANATION:
Semiconductors have a small band gap, so heating frees more charge carriers and raises their conductivity.
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PRACTICE QUESTIONS
1. RIDDLE:
I am an element in group 14.
I am the most widely used material for computer chips.
My valency is four.
Sand is mostly my oxide.
A famous valley in California is named after me.
My symbol is Si.
Who am I?
ANSWER: SILICON
EXPLANATION:
Silicon is the main semiconductor of electronics.
2. RIDDLE:
I am a group 14 element just below silicon.
I was used in the first transistors.
My band gap is smaller than that of silicon.
Mendeleev predicted me as eka-silicon.
My symbol is Ge.
I am named after a European country.
Who am I?
ANSWER: GERMANIUM
EXPLANATION:
Germanium has a band gap of about 0.67 eV.
3. RIDDLE:
I am the absence of an electron in a bond.
I behave like a positive charge.
I am the main charge carrier in p-type material.
I drift opposite to electrons in an electric field.
Heat creates me together with a free electron.
I am named after an empty space.
Who am I?
ANSWER: HOLE
EXPLANATION:
A hole is a vacancy that moves like a positive charge.
4. RIDDLE:
I am an energy range with no allowed electron states.
I separate the valence levels from the conduction levels.
Insulators have a wide one of me.
Silicon's value of me is about 1.1 eV.
Light with enough energy can bridge me.
Metals have none of me.
Who am I?
ANSWER: BAND GAP
EXPLANATION:
A small band gap makes a semiconductor.
5. RIDDLE:
I am a two-terminal device.
I let current flow in one direction only.
I am made from one p–n junction.
I rectify alternating current.
My symbol is an arrow against a bar.
A silicon one of me needs about 0.7 V to conduct.
Who am I?
ANSWER: DIODE
EXPLANATION:
A diode conducts in forward bias only.
6. RIDDLE:
I am a three-terminal device.
My terminals may be called emitter, base and collector.
I can act as an amplifier or a switch.
Billions of me are packed into a computer chip.
Bardeen, Brattain and Shockley invented me in 1947.
I replaced the vacuum tube.
Who am I?
ANSWER: TRANSISTOR
EXPLANATION:
A small base current controls a large collector current.
7. RIDDLE:
My resistance responds strongly to heat.
My resistance usually falls as temperature rises.
I am used in electronic thermometers.
I am made of semiconducting material.
My common type is called NTC.
I can switch on a fan when a room gets hot.
Who am I?
ANSWER: THERMISTOR
EXPLANATION:
An NTC thermistor has a negative temperature coefficient.
8. RIDDLE:
My conductivity is extremely low.
My band gap is very wide.
Rubber and glass are examples of me.
Electric cables are coated with me.
My electrons are tightly bound.
I am the opposite of a conductor.
Who am I?
ANSWER: INSULATOR
EXPLANATION:
Almost no electrons can cross a wide band gap.
9. RIDDLE:
I am the range of energy levels where electrons move freely.
I lie above the valence levels.
Electrons reach me when they cross the gap.
In metals I overlap the valence levels.
Electrons in me carry current.
I am nearly empty in a cold semiconductor.
Who am I?
ANSWER: CONDUCTION BAND
EXPLANATION:
Electrons in the conduction band are free to move.