(a) What total (excess) charge q must the disk in Figure 22-13 have for the elec

Question

(a) What total (excess) charge q must the disk in Figure 22-13 have for the electric field on the surface of the disk at its center to have magnitude 3.0 106 N/C, the E value at which air breaks down electrically, producing sparks? Take the disk radius as 1.4 cm, and use the listing for air in Table 22-1. C (b) Suppose each surface atom has an effective cross-sectional area of 0.015 nm2. How many atoms are needed to make up the disk surface? atoms (c) The charge in (a) results from some of the surface atoms having one excess electron. What fraction of the surface atoms must be so charged?

Explanation / Answer

Solution:-

Electric field on the surface of the disk atits center = E

= s/2e0

= 3 * 106N/c
with s= q/A
so q = sA

= spR2
q =2Ee0 pR2
but disk radius R = 4.1cm

= 4.1 *10-2m
q = 2pe0pR2

=R2E/2k ( 1/4pe0

= k so2pe0

= 1/2K
q = (4.1 * 10-2m )2*3 * 106 N/c)/2 * 8.99 * 109Nm2/C2
solve q = -------C

ANSWER:-
C) q/Ne
where N = 3.52 * 1017 atoms , e = 1.6 *10-19C

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