Q.

If potential (in volts) in a region is expressed as V(x,y,z)=6xy-y+2yz, the electric field (in N/C) at point (1, 1, 0) is      [2015]

1 -(2i^+3j^+k^)  
2 -(6i^+9j^+k^)  
3 -(3i^+5j^+3k^)  
4 -(6i^+5j^+2k^)  

Ans.

(4)

The electric field E and potential V in a region are related as E=-[Vxi^+Vyj^+Vzk^]

Here, V(x,y,z)=6xy-y+2yz 

E=-[x(6xy-y+2yz)i^+y(6xy-y+2yz)j^+z(6xy-y+2yz)k^]

         =-[(6y)i^+(6x-1+2z)j^+(2y)k^]

At point (1, 1, 0),

E=-[(6(1))i^+(6(1)-1+2(0))j^+(2(1))k^]=-(6i^+5j^+2k^)