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## Numerical Problems from Pressure, Density and Floatation

1. Ramesh buys 6 bottles of syrup each containing 1litre. Each empty bottle weighs 400g. The density of syrup is 1.2 g/cm3. What weight does Ramesh have to carry home?

2. The volume of 900g of a substance is 1000 cm3. Will the substance sink or float in water if the density of water is 1g/cm3. What will be the mass of water displaced by the substance?

## Why direct currents aren’t used in Home circuits?

How can an alternating current change its direction while moving in a wire or any conductor? Why direct currents aren’t used in Home circuits?

Alternating current is produced by rotating a coil in a strong magnetic field (or by rotating magnet around the coil)

So, during every half rotation the direction of emf (voltage) induced in the coil reverses and hence the current too reverses its direction. The frequency of ac in India is 50 Hz and therefore in every 1 sec there will be  100 changes in direction.

Alternating currents are suitable for long distance as it can be stepped up using transformer to minimize energy loss and can be stepped down for use at home.

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