Advertisements
Advertisements
प्रश्न
The table below shows the current in three different electrical appliances when connected to the 240 V mains supply:
| Appliance | Current |
| Kettle | 8.5 A |
| Lamp | 0.4 A |
| toaster | 4.8 A |
- Which appliance has the greatest electrical resistance? How does the data show this?
- The lamp is connected to the main supply by using a thin, twin-cored cable consisting of live and natural wires. State two reasons why this cable should not be used for connecting the kettle to the mains supply.
- Calculate the power rating of the kettle when it is operated from the 240 V mains supply.
- A main takes the kettle abroad where the mains supply is 120 V. What is the current is the kettle when it is operated from the 120 V supply?
Advertisements
उत्तर
(a) The lamp has the greatest electrical resistance because the current drawn by it is the least.
`R=V/I`
and hence resistance varies inversely with the current.
(b) The reasons for this are as follows:
- The kettle draws a large amount of current. So the wire may melt down due to heating.
- For the device to be safe, it needs to be have an earthing system. This is missing here.
(c) The power, P will be:
Given - V = 240 V, I = 8.5 A
P = VI
P = 240 V × 8.5 A
P = 2040 W
(d) V1 = 240, V2 = 120 V, I1 = 8.5, I2 = ?
V = IR
`therefore "V"_1/"V"_2 = "I"_1/"I"_2`
`therefore 240/120 = 8.5/"I"_2`
`therefore 2 = 8.5/"I"_2`
`therefore "I"_2 = 8.5/2`
`therefore "I"_2 = 4.25`
APPEARS IN
संबंधित प्रश्न
Define Electric power.
If a bulb of 60W is connected across a source of 220V, find the current drawn by it.
Which one has a higher electrical resistance : a 100 watt bulb or a 60 watt bulb?
Write an expression for the electrical power spent in flow of current through a conductor in terms of
(a) Resistance and potential difference, (b) current and resistance.
An electrical appliance having a resistance of 200Ω is operated at 200 V. Calculate the energy consumed by the appliance in 5 minutes (i) in joules (ii) in kWh.
The diagram below shows a magnetic kept just below the conductor AB which is kept in North South direction.
(i) In which direction will the needle deflect when the key is closed ?
(ii) Why is the deflection produced ?
(iii) What will be the change in the deflection if the magnetic needle is taken just above the conductor AB ?
(iv) Name one device which works on this principle.
State the S.I. units of electrical power and electrical energy.
(i) Define the household unit of electricity.
(ii) What is the voltage of the electricity that is generally supplied to a house?
Which cable, one rated 15A and the other rated 5A will be thicker? Give a reason.
Mention three uses of the carbon arc.
What changes in energy occur in an electric bulb?
State two advantages of filling an inert gas in an evacuated electric filament lamp.
If the rating of an electric bulb is 100W – 230V, Explain its meaning.
An electric bulb is marked 100 W, 230 V. What does this mean?
What is the order of current drawn by appliances connected to the ‘power circuit’ of a household?
Establish the relation that heat produced in a metallic conductor due to the flow of current is V2t/R joules, where V is the potential difference across the ends of the conductor, R its resistance and t is the time in second for which current flows.
Out of the three fuses with current ratings 5A, 10A, 15A, which one is to be connected in a geyser circuit marked 3 kW, 220V? Give reason for your answer.
Two bulbs are rated: bulb A 100W, 120 V bulb B 10W, 120 V. If both are connected across a 120V supply, which bulb will consume more energy, When in series? Also calculate the current through each bulb in above cases.
An electrical appliance is rated 1500 W, 250 V. This appliance is connected to 250 V mains. Calculate:
(i) the current drawn,
(ii) the electrical energy consumed in 60 hours,
(iii) the cost of electrical energy consumed at Rs. 2.50 per kWh.
What is the commercial unit of electrical energy? Represent it in terms of joules.
