QUARTER FINAL STAGE 2024
YILO KROBO
KOFORIDUA SENIOR HIGH TECH
KNUST SHS
ROUND 5 - RIDDLE
RIDDLE
I am a physical quantity
I am a scalar quantity
I am dimensionless
I express a speed in terms of a fundamental speed
I equal the ratio of the sines
WHO AM I?
ANSWER: REFRACTIVE INDEX
EXPLANATION:
Refractive index is a dimensionless scalar.
$n = \dfrac{c}{v} = \dfrac{\sin i}{\sin r}$.
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PRACTICE QUESTIONS
1. RIDDLE:
I am measured in degrees.
I exist only when light goes from a denser to a less dense medium.
At me, the refracted ray grazes the boundary.
Beyond me, all the light is reflected.
My sine equals $\dfrac{1}{n}$ for a medium in air.
For glass of index 1.5 I am about 42°.
Who am I?
ANSWER: CRITICAL ANGLE
EXPLANATION:
$\sin c = \dfrac{1}{n}$.
2. RIDDLE:
I am a length.
I am how deep a pool looks from above.
I am less than the real value when viewed from air.
I equal the real value divided by the refractive index.
I make swimming pools look shallower than they are.
A coin in water seems raised because of me.
Who am I?
ANSWER: APPARENT DEPTH
EXPLANATION:
$d_{\text{apparent}} = \dfrac{d_{\text{real}}}{n}$.
3. RIDDLE:
I measure how far a ray is turned from its original path.
A prism produces me.
I am least when the ray passes symmetrically through a prism.
My minimum value helps find the refractive index of the prism.
I am measured in degrees.
Violet light has a larger value of me than red light.
Who am I?
ANSWER: ANGLE OF DEVIATION
EXPLANATION:
At minimum deviation, $i = e$.
4. RIDDLE:
I am the distance between two neighbouring crests.
My symbol is λ.
I get shorter when light enters glass.
My product with frequency gives the wave speed.
Red light has a longer value of me than blue light.
I am measured in metres or nanometres.
Who am I?
ANSWER: WAVELENGTH
EXPLANATION:
$v = f\lambda$, and f stays the same on refraction.
5. RIDDLE:
I count the waves passing a point each second.
I am measured in hertz.
I do not change when light passes from air into water.
My symbol is f.
I decide the colour of light.
I equal speed divided by wavelength.
Who am I?
ANSWER: FREQUENCY
EXPLANATION:
The source fixes the frequency.
6. RIDDLE:
I am the fastest thing in the universe.
In a vacuum I am about $3.00\times10^{8}$ m/s.
I am smaller in glass than in air.
My value in a vacuum divided by my value in a medium gives n.
Einstein said I am the same for all observers.
My symbol is c.
Who am I?
ANSWER: SPEED OF LIGHT
EXPLANATION:
$n = \dfrac{c}{v}$.
7. RIDDLE:
I am measured from the normal.
I am formed by the incoming ray and the normal.
My sine divided by the sine of the refracted one gives n.
The law of reflection says I equal my reflected partner.
Above the critical value of me, total internal reflection occurs.
My symbol is i.
Who am I?
ANSWER: ANGLE OF INCIDENCE
EXPLANATION:
$n = \dfrac{\sin i}{\sin r}$.
8. RIDDLE:
I am a sideways shift.
A ray leaving a parallel-sided glass block shows me.
The ray comes out parallel to its first direction but moved over.
I increase with the thickness of the block.
I grow as the ray strikes the block more obliquely.
I am zero at normal incidence.
Who am I?
ANSWER: LATERAL DISPLACEMENT
EXPLANATION:
The emergent ray is parallel to the incident ray.
9. RIDDLE:
I am not the same as mass per unit volume.
A material with more of me slows light more.
Glass has more of me than water.
Light bends towards the normal on entering a medium with more of me.
Refractive index measures me.
Diamond has a very high value of me.
Who am I?
ANSWER: OPTICAL DENSITY
EXPLANATION:
A higher refractive index means a lower speed of light.