In a voltage circuit, the voltage remains the same. Thus when we add or remove the lamp, the total voltage at X will still remain the same. As a result, Z will light with the same brightnessView attachment 38869
since x and y are parallel there resistance is less.........so when y is removed the resistance across x increeases..and so does the voltage...as x and z are arranged in series so voltage across z decreases so it becomes less brighter......brightness depends on voltage