# Energy Engineering Questions and Answers – Wave Energy

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This set of Energy Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Wave Energy”.

1. Kinetic energy that results from the oscillation of water is called ________
a) Wave energy
b) Tidal energy
c) Ocean thermal energy
d) Hydro energy

Explanation: Kinetic energy that results from the oscillation of water is called wave energy. Wave energy is derived from wind energy, which derives in turn from solar energy. Wave energy can be much more concentrated than the solar energy.

2. How is height of wave determined?
a) By wind speed
b) By force of wave
c) By a immersion scale
d) By a floating device

Explanation: Wave height is determined by wind speed, the duration of time the wind has been blowing, fetch and by the depth and topography of the seafloor. A given wind speed has a matching practical limit over which time or distance will not produce larger waves.

3. What does oscillatory motion at ocean produce?
a) Microseisms
b) Froth
c) Disturbance of currents
d) Currents

Explanation: Oscillatory motion is highest at the surface and diminishes exponentially with depth. However, for near a reflecting coast, wave energy is also present as pressure oscillations at great depth, producing microseisms.
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4. Waves are caused indirectly by ______
a) Wind energy
b) Solar energy
c) Geo-thermal energy
d) Wave energy

Explanation: Like the wind and OTEC, ocean and sea waves are caused indirectly by solar energy. Waves are caused by the wind, which in turn is caused by the uneven solar heating and subsequent cooling of the earth’s crust and the rotation of the earth.

5. Select the correct formula of potential energy in wave energy?
a) $$\frac{PE}{A} = \frac{1}{4}ρa^2 × \frac{g}{g_c}$$
b) PE = $$\frac{1}{4}ρa^2 × \frac{g}{g_c}$$
c) $$\frac{A}{PE} = \frac{1}{4}ρa^2 × \frac{g}{g_c}$$
d) $$\frac{PE}{A} = \frac{1}{4}$$ρa2 × g

Explanation: $$\frac{PE}{A} = \frac{1}{4}ρa^2 × \frac{g}{g_c}$$ is the correct formula for the potential energy of a wave.
g = gravitational acceleration, m/s2
gc = conversion factor
ρ = water density
a = amplitude
A = λL in J/m2.
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6. Select the correct formula of kinetic energy of a wave?
a) $$\frac{KE}{A} = \frac{1}{4}ρa^2 × \frac{g}{g_c}$$
b) KE = $$\frac{1}{4}ρa^2 × \frac{g}{g_c}$$
c) KE = $$\frac{1}{4}ρa^2$$
d) $$\frac{KE}{A} = \frac{1}{4}ρa^2$$

Explanation: The correct formula for kinetic energy of a wave is $$\frac{KE}{A} = \frac{1}{4}ρa^2 × \frac{g}{g_c}$$.
g = gravitational acceleration, m/s2
gc = conversion factor
ρ = water density
a = amplitude
A = λL in J/m2.

7. What are used to reduce to reduce the motion of floats?
a) Back pressure
b) Tubes
c) Damping fins
d) Anchor

Explanation: Damping fins are used to reduce the motion of the floats. The platform is stabilized within the water by four large underwater floatation tanks so that it is supported by the buoyancy forces. The floatation tank’s surfaces are wider in appearance and are flat.

8. From what material is the float (platform) made of _____________
a) Molded plastic
b) Thermocole
c) Stainless steel
d) Tubes

Explanation: The platform is made of molded plastic with s foamed plastic core to arrive at the required density and strength. It is also called float since it floats on the water. And it is in shape of cylinder with wide and flat bottom surface.

9. A _______ attached to the float moves up and down inside a cylinder.
a) chain
b) barrel
c) piston

Explanation: A piston attached to the float moves up and down inside a cylinder, fixed to the platform and is therefore relatively stationary. This piston cylinder arrangement is used as a reciprocating air compressor.

10. What type of energy is wave energy?
a) Non – conventional
b) Commercial
c) Non – renewable
d) Exhaustible

Explanation: Wave energy is free and non-conventional source of energy. Harnessing of energy by this method is relatively pollution free and because they remove energy from the waves, leaves the water in a relatively placid state in their wakes.

11. What is major disadvantage of wave energy?
a) It is not efficient enough
b) It is available only in ocean
c) The harnessing cost is more
d) Unstable during high wind pressures

Explanation: The major disadvantage of wave energy is that the energy is available on the ocean. The extraction equipment must be operated in a marine environment with all that implies in terms of maintenance, construction cost, life time and reliability.

12. Motion of water in a wave is primarily ________
a) Vertical
b) Horizontal
c) Linear
d) Opposite

Explanation: Wave motion is primarily horizontal but the motion of the water is vertical. Mechanical power is obtained by floats making use of the motion of water. The concept visualizes a large force that is driven up and down by the water within relatively stationary guides.

13. How many number of manifolds are part of a platform of floating device?
a) 1
b) 2
c) 3
d) 4

Explanation: There are four manifolds that are part of a platform. There are four large under water floatation tanks which stabilize the platform. Platform is supported by buoyancy forces and no vertical or horizontal displacement occurs due to wave action.

14. Which device uses the float which has two motions?
a) High level reservoir wave machine
b) Dolphin type wave generator
c) Hydraulic accumulator
d) Float wave power conversion device

Explanation: Dolphin type uses the float which has two motions. The first is a rolling motion about its own fulcrum with the connecting rod. Revolving movements are caused between the float and the connecting road. The other is nearly vertical or heaving motion about the connecting rod fulcrum.

15. In which wave machine instead of compressing air, the water itself is pressurized?
a) High level reservoir wave machine
b) Dolphin type wave generator
c) Hydraulic accumulator
d) Float wave power conversion device

Explanation: Hydraulic accumulator wave machines, instead of compressing air, the water itself is pressurized and stored in a high pressure accumulator or pumped to a high level reservoir, from which it flows through a water turbine electric generator.

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