# Basic electricity & incandescent bulb numericals

• flabber
In summary, the conversation discusses four different numerical problems related to electricity and electrical components. These include determining the value of n in order for a 12V, 24W tungsten filament bulb to run at its rated power, identifying which bulb will burn most brightly when connected in series or parallel across 220V mains, calculating the units consumed by an electric iron marked at 20V and 500W when used for 24 hours, and finding the heat generated by a 40W bulb in one hour. The participants also discuss the importance of showing one's own efforts in solving problems and suggest posting separate questions in separate threads to avoid confusion.
flabber
hi there, i hav few questions:

1. A 12V, 24W tungsten filament bulb is supplied with current from n cells connected in series. Each cell has an emf of 1.5V and internal resistance of 0.25. What is the value of n in order that the bulb runs at its rated power?

2. Three bulbs are rating 40W, 60W, 100W designed to work on 220V mains. Which bulb will burn most brightly if they are connected in SERIES across 220V mains? Repeat the same question when they are connected in PARALLEL across 220V.

3. An electric iron is marked 20 Volts, 500W. what will be The units consumed by it in using it for 24 hours?

4. What is the heat generated by a 40 W bulb in one hour?

please someone help me wid these numericals, i wud be highly grateful!

Show some workout.
Can you find out the relation between V, W, I and R?

flabber, welcome to PF

In addition to showing your own efforts towards solving the problem, please post separate questions in separate threads. If we had 4 problem discussions all running at once, it would be too confusing to follow.

I'll suggest you make 4 separate new posts, one for each problem. Also, please show what equations you think are relevant (as rl.bhat suggested), and show your own attempt or start toward solving each problem.

Last edited:

## 1. How do I calculate the resistance of a wire?

The resistance of a wire can be calculated using Ohm's Law, which states that resistance is equal to the voltage divided by the current. This can also be represented as R = V/I, where R is resistance, V is voltage, and I is current. To calculate the resistance of a wire, you will need to know the voltage and current values.

## 2. What is the relationship between current and voltage in an incandescent bulb?

The relationship between current and voltage in an incandescent bulb is directly proportional. This means that as the voltage increases, the current also increases. This is because the filament in the bulb has a higher resistance as the temperature increases, leading to an increase in current flow.

## 3. How do I calculate the power of an incandescent bulb?

The power of an incandescent bulb can be calculated using the formula P = VI, where P is power, V is voltage, and I is current. This formula is derived from the fact that power is equal to the product of voltage and current. To calculate the power of an incandescent bulb, you will need to know the voltage and current values.

## 4. What is the efficiency of an incandescent bulb?

The efficiency of an incandescent bulb is typically around 10-15%. This means that only 10-15% of the electrical energy supplied to the bulb is converted into light, while the rest is converted into heat. This is because incandescent bulbs use a filament that gets hot and emits light, rather than using a more efficient method like LED bulbs.

## 5. How do I calculate the cost of operating an incandescent bulb?

The cost of operating an incandescent bulb can be calculated using the formula Cost = Power x Time x Cost per kWh. This formula takes into account the power of the bulb, the amount of time it is in use, and the cost per kilowatt-hour of electricity. To calculate the cost, you will need to know these three values, which can typically be found on your electricity bill.

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