Leaving Cert Physics Work, Energy & Power: Read the following passage and a

Question

Read the following passage and answer the accompanying questions.

Windmills have been used for thousands of years to grind grain but the first attempts to use wind turbines to generate electricity were not made until the late 1800s. Viable large scale wind turbines were not produced until the 1980s. At the moment about 12% of Ireland's electricity needs are met by wind energy and it is planned to increase this to 33% by 2020.

Wind is a source of renewable energy and is now one of the most cost-effective methods of electricity generation.

The power of the wind can be calculated from $P = \frac{1}{2} \rho A v^3$ where $\rho$ is the density of the air, $A$ is the area the wind acts on and $v$ is the speed of the wind. In theory it is possible to extract 58\% of this energy in a wind turbine. Much of the loss occurs as the wind is slowed down rather than stopped as it passes the turbine.

The rotating blades of the turbine transfer their energy to an a.c. generator, which produces electricity by electromagnetic induction. The resulting alternating supply has to be changed to match the 230 V, 50 Hz that is used for electrical supply in Ireland.

Many people are concerned about the noise associated with wind turbines. Better blade construction has led to reduced noise. At about 150 m from the turbine, sound intensity levels are 45 dB. This reduces to 42 dB at about 200 m away. These values compare favourably with values of around 60 dB in a busy office.

(Adapted from: Renewable Energy, Edited by Godfrey Boyle, Oxford University Press in association with The Open University.)

Read the following passage and answer the accompanying questions - Leaving Cert Physics - Question 11 - 2012

Worked Solution & Example Answer:Read the following passage and answer the accompanying questions - Leaving Cert Physics - Question 11 - 2012

What is the effect on the power of the wind if the wind speed is doubled?

Why is it not possible to extract all of the energy in the wind striking a wind turbine blade?

What is electromagnetic induction?

How is the output voltage of a wind turbine changed to 230 V a.c.?

Estimate the factor by which the sound intensity changes when you move from a position which is about 200 m away to a position which is about 150 m away from a typical wind turbine.

What is the tip speed (the linear velocity of the outer end) of a blade of radius 30 m when it completes a revolution every 3 seconds?

Small scale wind turbines are sometimes used to charge batteries. The a.c. output voltage has to be converted to a d.c. voltage. How is this achieved?

Name one other renewable source of energy.

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