Applied Science question #3

 

I spotted this large solar panel on a farm from the train to Carlisle. It is not long after you leave Wigton. You can only see the back of it. It is the tilted rectangle on the pole. Assuming that the intensity of the sunlight is 1000W per square metre, calculate the number of Units of electricity generated THIS WEEK. At 12p a Unit, estimate how much money it might save them a year.

L6 estimation question #5: Fountains at Rydal Hall

 

The water follows a parabolic curve. It is an example of projectile motion. I want you to calculate the initial velocity of the water. To do that, you need to calculate the constant horizontal speed and the initial vertical speed. Combine them by Pythagoras to get the overall initial velocity.

Hint: The initial vertical speed is the same as the final vertical speed with which it hits the surface of the water, assuming no air resistance. So do the second half of the projectile motion, from the top of the curve downwards to make it like the problems we normally do. 

Polarised in Ambleside

 

These two pictures of the House on the Bridge in Ambleside were taken through my polarising sunglasses. I twisted the glasses through 90 degrees between the photographs. It shows that at the angle between me and the water, the reflected light from the water is polarised. There is little reflected sunlight from the surface of the water in the first picture but a lot in the second picture. Light is a transverse wave which means that the direction of propagation of the energy is at 90 degrees to the direction of oscillation. In other words, the waves vibrate side to side. A polarising filter is modelled as a slits through which waves have to pass. If they vibrate side to side in line with the slits, the light gets through. That's the second picture. Twisting the slits through 90 degrees means that the waves now vibrate across the slits and can't get through. Sound is a longitudinal wave: the direction of propagation of energy is in line with the direction of oscillation. It can never vibrate across the line of the slits so can never be polarised. (Please note: slits is a way of explaining. In truth, in a plastic polarising filter it is about long chain molecules absorbing waves in one direction but not at 90 degrees)

Hartlepool nuclear power station

 

This is a picture of Hartlepool nuclear power station. It works by having the nuclei of uranium atoms split when neutrons are fired at them. This process is called fission. When a nucleus splits, it releases thermal energy which heats up a material called the coolant. The coolant transfers thermal energy into water by conduction between pipes. The water boils to make steam which drives a turbine. A much advertised advantage of nuclear power is that nothing burns so no carbon dioxide or sulphur dioxide are released as chemical pollution into the air. A disadvantage is that radioactive waste is produced that will be dangerous for thousands of years. At the moment, this is sent to Sellafield to be treated and stored. This nuclear power station generates 1, 190 Megawatts of electrical power. If you were asked to compare nuclear power to wind power, they both have in common that they do not release chemical pollution into the air. I found some data that claims that there are 4366 wind turbines on land in the UK and that they generate 7,172 Megawatts of electrical power. http://www.renewableuk.com/en/renewable-energy/wind-energy/uk-wind-energy-database/index.cfm Clearly this depends on the weather and how much the wind is blowing. Just so you know, peak demand for electrical power in the UK is 60,000 Megawatts (60 Gigawatts).

Soft landing in Berlin

 

This is undercarriage from an American DC3 used in the Berlin airlift. Notice that the pole attached to the wheel is designed to go up into the grey tube above it. There will be suspension and shock absorbers. I'm not sure how the suspension is done in this case, but perusal of the Internet suggests that some modern aircraft use an airbag that compresses as the force of landing pushes the wheel up. This is like bending your knees when you jump down. It increases the time to stop which reduces the rate of change of momentum, thus decreasing the force of impact. Unless you include shock absorbers, it is likely that the suspension will spring backwards and forwards making the aeroplane wobble up and down. On a car, a shock absorber is a metal plate that gets dragged slowly through a viscous liquid. There are a lot of assumptions here. I didn't realise how little I knew about the specifics of aeroplane landing gear. The Physics is correct, though.

The closest I'll get to the Magdeburg hemispheres

 

When I realised that the coach was going past Magdeburg on the way to Berlin I got very excited. I tried to photograph the sign on the Autobahn but we were moving too quickly! So you get a picture of the outskirts of the town. It was at Magdeburg that they did a famous experiment about vacuums. They got two huge hollow steel hemispheres and put them together. The join was sealed with something airproof like Vaseline. There was water inside which was boiled. The steam was allowed out of a small hole and pushed the air out with it. The hole was sealed and the apparatus allowed to cool. The steam inside condensed to water leaving a pretty good vacuum inside. Two teams of horses couldn't pull the hemispheres apart because the high air pressure on the outside pushing in met no counter force from the vacuum. At least this is how it was told to me by my Physics teacher. Perhaps I should check that I've got all of the details correct...

Pumped storage at Loch Ness

 

The UK's coal-fired power stations take too long to get started to have them turned on and off on a regular basis. They run all the time, day and night. This is fine during the day but much less electricity is used a night. They generate power that is not used. There are several places in the country where the surplus electricity is used to pump water up hill. The water gains gravitational potential energy (mgh). The energy is stored until there is a shortage. The barriers are opened and the water flows back down hill through turbines that generate electricity again. The example photographed is on Loch Ness. The middle photograph shows the turbine shed in the distance. The water is pumped to Loch Mhor which is several miles away. The information says that there are two 150MW generators run by the turbines. It says that are peak flow, 200 tonnes of water flows every second. Use mgh to work out the gravitational potential energy lost in one second - this is the power input to the turbines. (You can get the heights by enlarging the bottom picture). Then work out the efficiency of the two turbine generators combined. (1 tonne = 1000kg. MW means Mega Watts which is 1 million Watts)