Physics
- A wire 50 cm long and 1 mm^2 in cross section carries a current of 4 A when connected to a 2 V battery .The resistivity of the wire is a) 4 x 10^-6 b) 1 x 10^-6 c) 2 x 10^-7 d) 5 x 10^-7
- The frequency of sinusodial wave y = 0.4cos[2000 t + 0.80] would be a) 1000 π Hz b) 2000 Hz c) 20 Hz d) 1000/π Hz
- The frequency of electromagnetic wave, which best suited to observe a particle of radius 3 x 10^-4 cm is of the order of a) 10^15 b) 10^14 c) 10^13 d) 10^12
- Which rays contain (positive) charged particles? a) α-rays b) β-rays c) γ-rays d)X-rays
- Half life of a radioactive element is 12.5 hour and its quantity is 256 g.After how much time its quantity will remain 1 g? a) 50 hrs b) 100 hrs c) 150 hrs d) 200 hrs
1) b)1 x 10^-6 { length l= 50 cm = 0.5 cm
Area A=1 mm^2 = 1x10^-6 m^2
Current I=4A and voltage V=2V
Resistace R=V/I =2/4 =0.5
Risistivity ρ = R x A/l = (0.5 x 1x10^-6) / 0.5 = 1 x 10^-6)
2) c) 1000/π hz { compare with equation y=acos(2πVt+φ)
this gives 2πV=1000/π Hz}
3) b)10^14 { the wave length of radiation used should be less than the size of the particle size of the particle =λ=C/ν
3 x 10^-4=(3x10^10)/ν or ν=10^14 Hz }
4)a) α-rays { α rays are positively charged particles }
5)b)100 hrs{N/N0 =(1/2)^n n= number of decays 1/256=(1/2)^8 =(1/2)^n where n=8 time for 8 half life=100 hrs
if any mistakes in this post feel free to notify us by commenting.
if any mistakes in this post feel free to notify us by commenting.
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