National Physical Laboratory of India users. This process, known as dissemination, is carried out in a number of ways. For applications requiring low levels of uncertainty, there is satellite based dissemination service, which utilizes the Indian national satellite, INSAT. Time is also disseminated through TV, radio, and special telephone services. The caesium atomic clocks maintained at NPL are linked to other such instituted all over the world through a set of global positioning satellites. The unit of electric current, ampere, is realized at NPL by measuring volt and Ohm separately. The uncertainty in measurement of ampere is ± 1 × 10. The standard of temperature
Electric current with formula_20 being the elementary charge and formula_21 the electron density. The carriers move in the direction of decreasing concentration, so for electrons a positive current results for a positive density gradient. If the carriers are holes, replace electron density formula_21 by the negative of the hole density formula_23. In linear anisotropic materials, "σ", "ρ" and "D" are tensors. In linear materials such as metals, and under low frequencies, the current density across the conductor surface is uniform. In such conditions, Ohm's law states that the current is directly proportional to the potential difference between two ends (across) of that