Physics - Online Test
Q1. The displacement of a particle executing S.H.M is given by y=0.25 sin 200 t cm. The maximum speed of the particle is
Answer : Option D
Explaination / Solution:
No Explaination.
Q2. 
A uniformly charged thin spherical shell of radius R carries uniform surface charge density of σ per unit area. It is made of two hemispherical shells, held together by pressing them with force F(See figure). F is proportional to
Answer : Option C
Explaination / Solution:
Outward electric field at the surface of shell is If Q is the charge on the shell and A is the area, than the outward pressure is Force=PX effective area of hemispherical shellSo
Q3. 64 water drops having equal charges combine to form one bigger drop. The capacitance of the bigger drop, as compared to that of smaller drop will be
Answer : Option D
Explaination / Solution:
Capacitance of the small drop of radius r and that of the big drop of radius R is The volume of 64 small drops = volume of 1 big dropThe ratio
Q4. Two charges A = -2.50 μC and B = 6.0 μC are at a distance of 1 meter from each other. Distance from A at which the electric field is zero in meters is
Answer : Option B
Explaination / Solution:
where x= distance of null point from small charge, d=distance between two charges, q2=bigger charge, q1=small charge, +1 for like charges and -1 for unlike charges
Q5. Four capacitors, each of capacitance 50 are connected as shown in the figure. If the voltmeter reads 100 V, the charge on each capacitor is
Answer : Option D
Explaination / Solution:
PD across each 50μF capacitor is 100 V ( reading of the voltmeter.)
Q6. A long, hollow conducting cylinder is kept coaxially inside another long, hollow conducting cylinder of larger radius. Both the cylinders are initially electrically neutral.
Answer : Option A
Explaination / Solution:
When the charge is given to inner cylinder than there is an electric field is produced between cylinders which is given byand due to this a potential difference is developed between two cylinders.
Q7. Three condensers of capacity 2 μF , 4 μF and 8 μF respectively, are first connected in series and then connected in parallel. The ratio of the equivalent capacitance in the two cases will be
Answer : Option D
Explaination / Solution:
Q8. Consider a neutral conducting sphere. A positive point charge is placed outside the sphere. The net charge on the sphere is then,
Answer : Option A
Explaination / Solution:
If a charge q is placed outside than the electric field lines incident on the conducting sphere , if some charge is developed due to thee lines than opposite surface becomes oppositely charge and the total charge becomes zero.
Q9. A capacitor of capacitance C = 2 is connected as shown in the figure. If the internal resistance of the cell is 0.5, the charge on the capacitor plates is
Answer : Option C
Explaination / Solution:
At steady state no current flows through the capacitor. The total resistance in the circuit =2+0.5=2.5Ω. Current I=V/R=2.5/2.5=1A. since no current flows through the 10 Ω resistor, the potential drop across it =0. The potential drop across the 2 Ω resistor = potential across the capacitor= I×2=2V.Charge on the capacitor Q= CV=(2μF)×(2V)=4μC.
Q10. Positive and negative point charges of equal magnitude are kept at ( 0,0,a/2) and (0,0,-a/2) respectively. The work done by the electric field when another positive point charge is moved from (-a,0,0) to (0,a,0) is
Answer : Option A
Explaination / Solution:
+Q charge is moving on equatorial line of dipole as shown in figure, since on equatorial line V=0 So W=0
+Q charge is moving on equatorial line of dipole as shown in figure, since on equatorial line V=0 So W=0
