The more current drawn from the source, the more voltage is
dropped across the resistor and less appears at the terminals.
This hypothetical resistor is referred to as the output
resistance of the device.Most electrical circuits also provide some kind of supply or signal (also usually a voltage) to another device (a voltmeter or oscilloscope). The input to such devices are often represented as a pair of open terminals or using ideal-voltmeter symbol - the implication being that no current flows in the device (but not always). In reality, some current will flow into whatever device is connected here. This fact may be represented by placing a hypothetical resistor across the input terminals through which current can pass. This is referred to as load or input resistance of the device.