# What happens in a filament lamp when a current flows through it?

## What happens in a filament lamp when a current flows through it?

A filament lamp is a common type of light bulb. It contains a thin coil of wire called the filament. This heats up when an electric current passes through it, and produces light as a result.

### What is the relationship between current and voltage for a filament bulb?

The relationship between current and voltage is direct – as voltage increases, current increases. The relationship between current and resistance is inverse. As resistance increases, current decreases (for a fixed voltage). The light bulb filament changes temperature and therefore changes resistance.

What effect will increasing the current through a filament bulb have on the graph?

What effect will increasing the current through a filament bulb have on the graph? It will curve because the temperature and resistance are rising.

How can you investigate how the current is related to the potential difference for a filament lamp?

In a filament bulb, the current does not increase as fast as the potential difference. Doubling the amount of energy does not cause a current twice as big. The more energy that is put into the bulb, the harder it is for the current to flow – the resistance of the bulb increases.

## Why do filament lamps have high resistance?

As the filament heats up, it is more difficult for the electrons to get through the filament because it’s atoms are moving so much, and because resistance measures how easily a current passes, the resistance goes up.

### What is the resistance of a filament lamp?

As the filament within an incandescent lamp heats up, there is a significant change in the resistance between the off state and when it is operating. A typical 60W bulb operating at 250 volts will consume 0.24 amps and have a resistance of 1041Ω or thereabouts.

What is the relationship between battery voltage and current?

The current in a circuit is directly proportional to the electric potential difference impressed across its ends and inversely proportional to the total resistance offered by the external circuit. The greater the battery voltage (i.e., electric potential difference), the greater the current.

Why doesn’t a filament bulb obey Ohm’s law?

The filament lamp does not follow Ohm’s Law. Its resistance increases as the temperature of its filament increases. So the current flowing through a filament lamp is not directly proportional to the voltage across it.

## Why do lightbulbs change resistance?

The resistance of a lamp increases as the temperature of its filament increases. The current flowing through a filament lamp is not directly proportional to the voltage across it. Resistance doesn’t increase directly because of Voltage.

### What 4 properties affect the amount of resistance in a wire?

There are 4 different factors which affect resistance:

• The type of material of which the resistor is made.
• The length of the resistor.
• The thickness of the resistor.
• The temperature of the conductor.

Does current increase with resistance in a filament lamp?

The current through a filament lamp is not directly proportional to the potential difference. This is because the filament gets hot, which causes the resistance to increase. More energy is needed to push the current through the filament. As the potential difference increases, the current no longer increases as much.

Why does the resistance of a filament lamp change as the current increases?

The resistance of a filament lamp increases as the potential difference increases because the filament becomes hot. The movement of electrons (which is what causes the current) makes the atoms inside the filament vibrate faster and this makes the filament heat up.

## How does the resistance of a filament lamp increase?

It contains a thin coil of wire called the filament. This heats up when an electric current passes through it, and produces light as a result. The resistance of a lamp increases as the temperature of its filament increases. The current flowing through a filament lamp is not directly proportional to the voltage across it.

### How is the current flowing through a filament lamp related to the voltage?

The current flowing through a filament lamp is not directly proportional to the voltage across it. This is the graph of current against potential difference for a filament lamp: 1 2

Why is ohm’s law true in a filament bulb?

This relationship is called Ohm’s Law and is true because the resistance of the resistor is fixed and does not change. A resistor is an ohmic conductor. In a filament bulb, the current does not increase as fast as the potential difference. Doubling the amount of energy does not cause a current twice as fast.

How to plot a graph of current against potential difference?

Plot a graph of current against potential difference for the diode. A semiconductor diode only allows current to flow in one direction. If the potential difference is arranged to try and push the current the wrong way (also called reverse-bias) no current will flow as the diode’s resistance remains very large.