How to work out the number of lamps in a set with given Voltage and Power.. Read Details

[iiDaannn]

A set of decorative lights consist of a string of lamps. Each lamp is rated at 5.0V, 0.40W and is connected in series to a 230V supply.

I need to find out the number of lamps in the set, so that each lamp operates at the correct rating.
As well as this, I need to find out what the resistance of each lamp would be.

They are the details that I have been given. Please give me some idea AND a possible solution.
Thanks :)

[factor-fiction]

From school I remember that:

- power in Watts= volts x amps
- resistance = voltage divided by current

I'm just guessing what you do next though. Maybe divide the 240 volts by the figure of 5 volts per bulb - that would give 48 bulbs

Then maybe total watts= 48 bulbs x 0.4= 19.6 watts

This may prompt further ideas

[rov1200]

The way I work out my consumption in my household is to calculate the power drawn from a socket in kW (amps) not the voltage. An electric Kettle can draw 3kW. Therefore the 3kW kettle would be the equivalent of 3000/.4 or 30,000/4 = 7,500 bulbs in current drawn. As factor30 says if you want to do an academic exercise you can use Ohm's Law.