Tag Archives: National 5

Measuring Instantaneous speed⤴

from @ Helpmyphysics

It is impossible to measure the speed of an object at an instant.
It is only possible to find the object’s speed over a small distance and time.
This is achieved using a light gate and a thin card of length say 10 cm.
When the card interrupts the light beam it turns off a light sensor and starts an electronic timer.
The timer stops when the card passes the light beam and the sensor picks up the light signal again.

The near instantaneous speed is calculated by:

Charge that capacitor!⤴

from @ Helpmyphysics

A capacitor can be used in a sensor circuit to switch on a transistor after a time interval.
Such a voltage divider circuit will act as a kind of timer.
The time the voltage across the capacitor reaches 0.7 v, to switch on the transistor, can be short or long depending on the size of the capacitance of the capacitor or the size of the resistor its being charged through.

To lengthen the time interval the resistance can be made bigger or the vakue of the capacitor’s capacitance can be made bigger.