KCET 2026 Physics Solved Paper

Concept:An electron in a uniform electric field experiences a constant force, producing uniform acceleration. The motion can be analysed using kinematic equations.Explanation:The electron starts from rest, so its initial velocity is$$u = 0$$The electric force acting on the electron is$$F = eE$$Using Newton's second law, $F = m_{e}a$, the acceleration becomes$$a = \frac{eE}{m_{e}}$$Substitute the given values:$$a = \frac{(1.6 \times 10^{-19})(2.0 \times 10^{4})}{9.11 \times 10^{-31}}$$$$a = \frac{3.2 \times 10^{-15}}{9.11 \times 10^{-31}} \approx 3.51 \times 10^{15} \ \mathrm{m\,s^{-2}}$$The distance covered is$$s = 1.5 \ \mathrm{cm} = 1.5 \times 10^{-2} \ \mathrm{m}$$Since the electron starts from rest, using$$s = \frac{1}{2} a t^{2}$$we get$$t = \sqrt{\frac{2s}{a}}$$Substitute the values:$$t = \sqrt{\frac{2(1.5 \times 10^{-2})}{3.51 \times 10^{15}}}$$$$t = \sqrt{8.55 \times 10^{-18}} \approx 2.9 \times 10^{-9} \ \mathrm{s}$$Answer:The time taken is approximately $2.9 \times 10^{-9} \ \mathrm{s}$, which matches option A.