Solution for question number 1,
Let:Magnification=M
M= 2.
Object distance=U
U=25cm..
Image distance = V
V=unknown, let it be equal
to V.
From M=V/U,
M x U = (V/U) x U,
V=M x U
V=2 x 25cm,
V=50cm.
If M=4, making U the subject of the formular (since it is the required physical quantity to be found),
then U=50cm/4.
U=12.5cm.
Therefore, to provide a magnification of four times, An object must be placed at 12.5cm from the convex lens.
Solution question number 2,
Using pressure law,
Let P=pressure
Initial pressure P1 = 1.5 x 10^5Pa
Final pressure=unknown, let it be equal to P2,
Initial temperature=T1=-30°c=(-30+273)K,
T1=243K.
Final temperature=T2=25°c=(25+273)K,
T2=278K
since pressure law states that the Pressure of a fixed volume of a gas is directly proportional to it's absolute temperature,
P=KT., P1/T1=P2/T2=P3/K3=K = ... ... ,
P1/T1=P2/T2.
(P1/T1) x T2 = (P2/T2) x T2,
P2 = (P1/T1) x T2
P2=(1.5 x 10^5Pa ÷ 243K) x 298K,
P2 is approximately equally to
1.84 x 10^5Pa.
Therefore, the new pressure of the gas is approximately equal to 1.84 x 10^5Pa.