Question

An Ebonite rod, when rubbed with wool, acquires a negative charge of 4.0 × 10^-9 C. How many free electrons can constitute this much charge? Given that charge on an electron, e = -1.60 × 10^-19 C.​

Answer 1

Given :

• Charge on Ebonite rod, Q = $\sf -4.0 \times 10^{-9}C$
• Charge on an electron, e = $\sf -1.60 \times 10^{-19}C$

To Find :

• Number of free electrons in Ebonite rod, n = ?

Solution :

We are given :

• Charge on Ebonite rod, Q = $\sf -4.0 \times 10^{-9}C$
• Charge on an electron, e = $\sf -1.60 \times 10^{-19}C$

So, to find number of free electrons in Ebonite rod, we know that :

$\bull \: \: \: \: \underline{\boxed{ \pink{\bf n = \dfrac{Q }{e} }}} \: \pink{\dag}$

By substituting values :

$\sf : \implies n = \dfrac{-4.0 \times 10^{-9}C}{ - 1.60 \times 10^{-19}C} \\ \sf : \implies n = \dfrac{4.0 \times 10^{-9}}{1.60 \times 10^{-19}} \: \: \: \: \: \: \\ \sf : \implies n = \dfrac{4.0 \times 10^{19}}{1.60 \times 10^{9}} \: \: \: \: \: \: \: \: \: \: \\ \sf : \implies n = \dfrac{4 \times 10^{19}}{1.6 \times 10^{9}} \: \: \: \: \: \: \: \: \: \: \: \: \\ \sf : \implies n = \dfrac{4 \times 10^{10}}{1.6} \: \: \: \: \: \: \: \: \: \: \: \: \: \\ \sf : \implies n = 2.5\times 10^{10} \: \: \: \: \: \: \: \: \: \:$

$\underline{ \tt Hence, \: Answer \: is \: \pink{ \bf 2.5\times 10^{10}}}.$

Answer 2

Answer:

Q = -4.0×10^-9 C

C = -1.60×10^-19 C

n=Q/e=-4.0×10^-9 /-1.60×10^-19

2.5 × 10^10