Electrons Are Accelerated to a Speed Of $4.0 \times 10 ^ { 4 } \mathrm {~m} / \mathrm { s }$

Multiple Choice

Electrons are accelerated to a speed of $4.0 \times 10 ^ { 4 } \mathrm {~m} / \mathrm { s }$ and are then aimed at a double-slit apparatus, where interference fringes are detected. If the electrons were replaced by neutrons, what speed must neutrons have to produce interference fringes with the same fringe spacing as that observed with the electrons? $\left( h = 6.626 \times 10 ^ { - 34 } \mathrm {~J} \cdot \mathrm { s } , m _ { \text {electron } } = 9.11 \times 10 ^ { - 31 } \mathrm {~kg} , m _ { \text {neutron } } = 1.675 \times 10 ^ { - 27 } \right.$ $\mathrm { kg }$ )

A) $2.2 \times 10 ^ { 1 } \mathrm {~m} / \mathrm { s }$
B) $9.3 \times 10 ^ { 2 } \mathrm {~m} / \mathrm { s }$
C) $7.3 \times 10 ^ { 7 } \mathrm {~m} / \mathrm { s }$
D) $1.7 \times 10 ^ { 6 } \mathrm {~m} / \mathrm { s }$