To find the value of l, we can use the formula for power (P):

P = Q / t

Given values:
Q = 8 kJ = 8,000 J
t = 1 sec

P = 8,000 J / 1 sec
P = 8,000 W

Now, we can use the formula for power in terms of voltage and current:

P = U * I

Given value:
U = 4 V

8,000 W = 4 V * I
I = 8,000 W / 4 V
I = 2 A

Finally, we can use the formula for power in terms of resistance (R) and current (I):

P = I^2 * R

Substitute the values:
8,000 W = (2 A)^2 R
8,000 W = 4 A^2 R
R = 8,000 W / 4 A^2
R = 2,000 Ohms

Therefore, the value of l (resistance) is 2,000 Ohms.