in a Millikan-type experiment, two horizontal charged plates are 2.6 cm apart. A latex sphere of 1.3 x 10^-15kg remains stationary between the plates when the potential difference between the plates is 400 V. The upper plate is charged positively

a) since the sphere is stationary the direction of the electrical force is upwards/downwards and the charge on the sphere is positive/negative

b) what is the electrical field intensity between the plates?

a) 1.5 x 10^4 N/C

b) 6.4 x 10^-13 N/C

c)6.5 x 10^-5 N/C

d) 4.2 x 10^-18 N.C

c) what is the charge on the sphere?

d) how many excess electrons were on the surface of the sphere

a) 5e

b)6e

c)7e

d)8e