An oxide coated filament is useful in vacuum tubes because essentially

  • A

    It has high melting point

  • B

    It can withstand high temperatures

  • C

    It has good machanical strength

  • D

    It can emit electrons at relatively lower temperatures

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$(i)$ $6.563 \times {10^{ - 19}}C$       $  (ii)$ $8.204 \times {10^{ - 19}}C$

$(iii)$ $11.50 \times {10^{ - 19}}C$       $ (iv)$ $13.13 \times {10^{ - 19}}C$

$(v)$ $16.48 \times {10^{ - 19}}C$       $ (vi)$ $18.09 \times {10^{ - 19}}C$

From this data the value of the elementary charge $(e)$ was found to be