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# pressure and temperature

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1. http://www.ocr.org.uk/Images/131309-...nian-world.pdf
I don't understand question 4cii from the paper above and i don't understand the mark scheme below either
http://www.ocr.org.uk/Images/135334-...world-june.pdf
2. (Original post by runny4)
http://www.ocr.org.uk/Images/131309-...nian-world.pdf
I don't understand question 4cii from the paper above and i don't understand the mark scheme below either
http://www.ocr.org.uk/Images/135334-...world-june.pdf
Ever been using an electrical shower when someone else flushes a toilet somewhere else in the house?

flow rate depends on pressure and pressure can vary.
3. (Original post by Joinedup)
Ever been using an electrical shower when someone else flushes a toilet somewhere else in the house?

flow rate depends on pressure and pressure can vary.
then what is the other point to do with temperature and how does flushing a toilet change pressure in terms of the physics of the water in the pipes and why does flow rate depend on pressure in terms of physics
4. (Original post by runny4)
then what is the other point to do with temperature and how does flushing a toilet change pressure in terms of the physics of the water in the pipes and why does flow rate depend on pressure in terms of physics
Well the points are that water pressure might change and water temperature might change.

The effect of pressure on flow rate should be familiar... have you ever done this demo

you've probably noticed water temperature changing in the summer when you have to run a tap for a minute until the water starts to come out cold.
5. (Original post by Joinedup)
Well the points are that water pressure might change and water temperature might change.

The effect of pressure on flow rate should be familiar... have you ever done this demo

you've probably noticed water temperature changing in the summer when you have to run a tap for a minute until the water starts to come out cold.
I just thought of a way of relating water pressure and temperature as PV=nRT so pressure is proportional to temp- is this valid.and i thought the temperature point is about the water getting hotter as it passes through the heater and this water heats up the room and the ambient temperature increases so the inlet temperature must increase from 17.4 degrees as the heater doesn't need to start from a temperature below the temperature of the room. Thank you for all your replies btw
6. (Original post by runny4)
I just thought of a way of relating water pressure and temperature as PV=nRT so pressure is proportional to temp- is this valid.and i thought the temperature point is about the water getting hotter as it passes through the heater and this water heats up the room and the ambient temperature increases so the inlet temperature must increase from 17.4 degrees as the heater doesn't need to start from a temperature below the temperature of the room. Thank you for all your replies btw
No PV=nRT is not useful here, that's applicable to gasses only. Liquid water is incompressible as far as we are concerned at A level. The volume of Liquid water is the constant at different pressures.

The way these showers work is that water is made to flow continuously through a box with an electrical heating element in it... which raises the temperature of the water.
The outlet water temperature depends on inlet water temperature and the flow rate, low flow rate means the water spends more time in the box being heated and comes out at a higher temperature, high flow rate means the water spends less time in the box being heated and comes out at a lower temperature.

There's usually a 'temperature control knob' on the control panel but it's actually a water flow control valve.

pressure is only important because any changes in the supply pressure affect the flow rate of water through the element.
7. (Original post by Joinedup)
No PV=nRT is not useful here, that's applicable to gasses only. Liquid water is incompressible as far as we are concerned at A level. The volume of Liquid water is the constant at different pressures.

The way these showers work is that water is made to flow continuously through a box with an electrical heating element in it... which raises the temperature of the water.
The outlet water temperature depends on inlet water temperature and the flow rate, low flow rate means the water spends more time in the box being heated and comes out at a higher temperature, high flow rate means the water spends less time in the box being heated and comes out at a lower temperature.

There's usually a 'temperature control knob' on the control panel but it's actually a water flow control valve.

pressure is only important because any changes in the supply pressure affect the flow rate of water through the element.
ok thank you

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