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A lamp has two resistances: a 'hot' resistance (its operating resistance) and its 'cold' resistance (its resistance when switched off), and the hot resistance is significantly higher than its cold resistance.
You can calculate its 'hot' resistance from its rated power and its rated voltage (assuming that it is being supplied at its rated voltage), by manipulating the following equation, to make Rthe subject: P= V2/R
You will, though, have to measure its cold resistance.
What else can I help you with?
What is meant by cold resistance of filament lamp?
It means exactly what it sounds like. The resistance of an incandescent bulb's filament depends on its temperature. A filament has a positive temperature coefficient, which means that its resistance increases as its temperature increases. A typical 40 watt bulb (120 volts) has a cold resistance of about 28 ohms, but its hot, operating resistance is about 360 ohms. If the cold resistance were constant, the bulb would dissipate 379 watts. In fact, cold turn on is the most stressful time for a bulb.
When the bulb is the resistance what this tells about the resistance?
An incandescent bulb has a filament that has a resistance. The value of the resistance determines the current that will flow for a given supply voltage. The heat generated by the current flowing through the filament gives off light. As the resistance of the filament decreases the current increases and you get more light.
What is the resistance of a lightbulb using Ohm's law?
By Ohm's law, resistance is voltage divided by current, so the resistance of a light bulb can be measured by observing the voltage across it simultaneously with observing the current through it. Interestingly, the hot resistance is significantly different that the cold resistance, so measuring resistance with an ohmmeter will not give a meaningful resistance. This is because the resistance of a light bulb has a positive temperature coefficient. Take a typical 60 W 120V light bulb, for instance... Its cold resistance is about 16 Ohms. Calculate current and power at 120 V and you get 7.5 A and 900 W. The truth is that at 60 W, the bulb pulls 0.5 A and has a resistance of 240 Ohms.
When two bulbes with 25W and 100W rated at 220V are connected in series with a supply of 440V which will fuse?
The 25w bulb, since it has the much higher resistance. The resistance can be derived from:P = V^2/RR = V^2/PFor the 100w bulb:R = 220^2/100 = 484 ohmsFor the 25w bulb:R = 220^2/25 = 1936 ohmsWhen connected in series, and then connected to 440V, the voltage across the 100w bulb would be:V = 440*484/(484+1936) = 88VThis is well within spec.The voltage across the 25w bulb would be:V = 440*1936/(484+1936) = 352vThis is way over spec, and would cause the bulb to fuse.Although this answer assumes that a light bulb is a linear resistor, they are not. The resistance of a light bulb changes significantly with voltage and filiament temperature. The 25w light bulb is still the one that fuses, but the non-linearity of the resistance needs to be understood.
Why is there zero current when a light bulb burns out?
there is no voltage and resistance
What is a fuse bulb?
a fuse bulb is a bulb in which the filament of the bulb burns and it stops working
Which has the thickest filament - a high-resistance or a low-resistance bulb?
A high-resistance bulb typically has a thicker filament compared to a low-resistance bulb. The thicker filament in a high-resistance bulb can withstand the greater heat generated by the increased resistance, resulting in a longer lifespan for the bulb.
An open fuse has a resistance of?
Zero. There is no resistance on an open fuse because there is no connection between the terminals on the fuse. I beg to differ There is INFINITE resistance in a BLOWN fuse... There is ZERO resistance in a GOOD fuse.
What is cold resistance?
That is e.g. the resistance of a cold bulb before the bulb is lighted and heats up.
What gives the biggest resistance 3 volt bulb or 6 volt bulb?
3 volt bulb gives the biggest resistance
How do we calculate the cold resistance of the bulb?
The cold resistance of a bulb can be approximated by measuring the resistance of the filament with a multimeter when the bulb is turned off and at room temperature. The resistance measured in this state can give an estimation of the cold resistance of the bulb. Keep in mind that this value may not be exact due to factors like the temperature coefficient of resistance and the non-linear behavior of the filament's resistance.
Does the resistance of a filament light bulb change as the bulb gets brighter?
Yes, the resistance of a filament light bulb increases as the bulb gets brighter. This is due to the increase in temperature of the filament, which causes the resistance to go up.
What does a light bulb have?
The resistance of a light bulb varies, depending on the type of bulb, the power rating, and the temperature. A typical incandescent 60 watt bulb, for instance has a cold resistance of about 30 ohms, and a hot resistance of about 240 ohms.
What is the general resistance of a tungsten filament?
The resistance of the filament in a light bulb is(voltage at which the bulb is designed to operate)2/(the rated power/watts of the bulb)
For bulbs connected in series the high watt bulb has high resistance?
No, the highest wattage bulb will have the lowest resistance.
Why does the resistance of a filament bulb depend on the current in the bulb?
The resistance of a piece of wire changes with temperature. In a filament bulb the wire is heated to about 3000 degrees C so a large change in resistance can be expected. A 240 v 105 w halogen bulb has a cold resistance of 35 ohms, but when running its resistance is 549 ohms.
Is the material inside a light bulb a conductor or resistance?
It has high resistance.
