Faraday cage. Museum worker sits in a cage which is being struck by a massive electrical discharge. The cage is designed so that no discharges will reach inside. The distance between the bars means that a discharge will always find it easier to hit a bar than pass in between to another object. The person inside is therefore protected. The discharge is created by a vast Van de Graaff generator (columns and spheres) behind the cage, with a potential difference of 2.5 million volts. Faraday cages are used to protect electrical equipment from lightning strikes. Photographed at the Franklin Institute, Philadelphia, USA.