Measuring Instruments

Stopwatches

• A stopwatch measures time intervals with a typical resolution of 0.01 s.
• Manual timing introduces significant uncertainty due to human reaction timeThe delay between observing an event and pressing the button, typically around 0.25 s. (approximately 0.25 s).
• This reaction time can be larger than the time interval being measured in fast experiments.
• To reduce the impact of reaction time: take repeat readings and calculate a mean, or time multiple oscillations and divide.

Light Gates

• Light gates are digital sensors consisting of an infrared transmitter and receiver positioned opposite each other.
• When an object blocks the beam, the signal is interrupted and a timer starts or stops.
• Light gates eliminate human reaction time errors, making them far more accurate than manual stopwatches.
• Speed can be calculated if two gates are placed a known distance apart: $\text{speed} = \frac{\text{distance}}{\text{time}}$
• Light gates can be connected to data loggers for automatic data collection and computer analysis.

Digital Instruments

• Digital instruments display readings as numerical values, making them easier to read and reducing parallax errorError caused by reading a scale from an angle rather than perpendicular to it..
• A top-pan electronic balance measures mass via a digital readout. It technically measures weight and calculates mass using $W = mg$.
• A digital multimeter can measure voltage, current, and resistance -- functioning as a voltmeter, ammeter, or ohmmeter.
• Multimeters can measure an enormous range of values, from microamps to kiloamps.
• Always check for zero errorsWhen an instrument gives a non-zero reading when the true value is zero. before starting measurements, even with digital instruments.