Question

The ratio of charge to mass of an electron in coulombs per gram was determined by J.J. Thomson. He determined this ratio by measuring the deflection of cathode rays in electric and magnetic fields. What value did he find for this ratio?

• A. $-1.76 \times 10^8$ coulombs/g
• B. $1.76 \times 10^{-8}$ coulombs/g
• C. $-1.76 \times 10^{10}$ coulombs/g
• D. $-1.76 \times 10^{-10}$ coulombs/g

Answer 1

Answer: (A)

Charge of an electron is
$=-1.6 \times 10^{-19} C$
Mass of electron is
$9.1 \times 10^{-31} kg =9.1 \times 10^{-28} g$
Thus, Charge/mass ratio is
$\frac{-1.6 \times 10^{-19}}{9.1 \times 10^{-28}}$
$=-1.76 \times 10^{8}$ coulombs $/ g$