What is necessary to obtain a spark across the gap between two electrodes?

To obtain a spark across the gap between two electrodes, it is essential that the circuit has high electromotive force (EMF). High EMF is required because it creates a sufficient voltage difference between the electrodes. When this voltage exceeds the dielectric breakdown strength of the medium between them (usually air), it allows the air to become conductive, resulting in a spark.

The breakdown voltage varies depending on factors such as the distance between electrodes and atmospheric conditions. Therefore, an adequate EMF is crucial in providing enough energy to ionize the air, thus facilitating the formation of a spark.

While factors like resistance and current flow can influence the overall circuit operation, they are not the primary requirement for generating the spark. A higher resistance (ohms) could limit current flow, while sufficient current flow alone doesn’t guarantee that the voltage is high enough to spark if the EMF is low. Impulse union is not a standard term relevant to generating sparks in this context, making it less applicable to the requirements for sparking in electrical circuits.