Y10 Physics - Electric Circuits

Why is a filament lamp non-ohmic

As the current increases, the filament's temperature increases. The metal ions vibrate more, causing more collisions with the electrons. This increases the resistance of the filament. Therefore current is no longer directly proportional to potential difference, so the lamp does not obey Ohm's Law.

Why is a diode non-ohmic

A diode only allows current to flow significantly in one direction. In the reverse direction it has a very high resistance, so little or no current flows. Therefore current is not directly proportional to potential difference.

Why does adding a resistor in series decrease curren

Adding another resistor increases the total resistance of the circuit. For a given potential difference, a greater resistance causes a smaller current.

Why is current the same everywhere in a series circuit

Current is the rate of flow of charge. In a series circuit there is only one path, so the same amount of charge passes each point every second.

Why is potential difference shared in a series circuit

The energy supplied by the battery is transferred between the components in the circuit, so the total potential difference is shared.

Why is potential difference the same across parallel branches

Each branch is connected directly across the power supply, so each branch experiences the full supply potential difference.

Why does adding a branch in parallel decrease total resistance

Adding another branch gives charge an additional path through the circuit. More current can flow for the same potential difference, so the total resistance decreases.

Why does current split in a parallel circuit

Charge can take different paths through the circuit, so the total current is shared between the branches.

Why does a thermistor's resistance decrease when temperature increases

As temperature increases, more charge carriers become available, allowing current to flow more easily. Therefore resistance decreases.

Why does a thermistor's resistance decrease when temperature increases

As temperature increases, more charge carriers become available, allowing current to flow more easily. Therefore resistance decreases

Why does an LDR's resistance decrease when light intensity increases

More light releases more charge carriers in the material, allowing current to flow more easily. Resistance therefore decreases.

Current

The rate of flow of charge

Potential difference

Energy transferred per unit charge

Resistance

A measure of how difficult it is for charge to flow through a component.

Ohmic conductor

A conductor for which current is directly proportional to potential difference, provided temperature remains constant.