18. Agar radiusi \( R \) bo'lgan zaryadlangan shar \( R / 2 \) radiusli zaryadlanmagan sharga tekkizilsa, birinchi sharning potensiali necha marta kamayadi? \( \begin{array}{llll}\text { A) } 1,2 & \text { B) } 1,5 & \text { C) } 2 & \text { D) } 0 \text { 'zgarmaydi }\end{array} \)

Zaryadlangan sharning potensiali quyidagi formula bilan hisoblanadi: \[ V = \frac{kQ}{R} \] bu yerda: - \( V \) - sharning potensiali, - \( k \) - elektrostatik doimiy (Coulomb doimiy), - \( Q \) - sharning zaryadi, - \( R \) - sharning radiusi. Birinchi shar radiusi \( R \) va zaryadi \( Q \) bo'lsa, uning potensiali: \[ V_1 = \frac{kQ}{R} \] Ikkinchi shar radiusi \( R/2 \) va zaryadi \( 0 \) bo'lgani uchun, u zaryadlangan sharga ta'sir qilmaydi. Zaryadlangan sharning potensiali ikkinchi shar radiusi bilan o'zgarmaydi, lekin ikkinchi shar radiusi \( R/2 \) bo'lganda, zaryadlangan sharning potensiali quyidagicha bo'ladi: \[ V_2 = \frac{kQ}{R/2} = \frac{2kQ}{R} \] Shuning uchun, zaryadlangan sharning yangi potensiali \( V_2 \) bo'ladi. Endi, potensialning kamayishini hisoblaymiz: \[ \text{Kamayish} = \frac{V_1}{V_2} = \frac{\frac{kQ}{R}}{\frac{2kQ}{R}} = \frac{1}{2} \] Demak, zaryadlangan sharning potensiali 2 marta kamayadi. Javob: **C) 2**.