How many electrons should be removed from a coin of mass 1.6 g, so that it may float in an electric field intensity of 109 N/C which is directed upwards?
Correct answer: A. 9.8 x 10^7
- A. 9.8 x 10^7
- B. 9.8 x 10^5
- C. 9.8 x 10^3
- D. 9.8 x 10^1
Explanation
To make the coin float, the upward electric force must equal the downward gravitational force. The gravitational force can be calculated using Fgravity = mg, where m = 1.6 g = 0.0016 kg and g = 9.8 m/s2. The electric force is Felectric = QE, where Q is the charge and E = 109 N/C. Setting Fgravity equal to Felectric, we have mg = QE. Solving for Q gives Q = (mg)/E = (0.0016 kg × 9.8 m/s2) / (109 N/C) = 1.568 × 10-8 C. The charge of an electron is approximately 1.6 × 10-19 C, so the number of electrons is Q/e = (1.568 × 10-8 C) / (1.6 × 10-19 C/electron) ≈ 9.8 × 107 electrons. Therefore, the correct answer is 9.8 × 107. The other options incorrectly calculate the number of electrons, leading to an imbalance of forces.
Report an error
The more specific you are, the faster it gets fixed. A source beats an opinion.
Prefer email? [email protected]
About Electrostatics
Electrostatics describes forces between charges through Coulomb's law, electric fields and field intensity, then uses electric potential to measure energy per unit charge. Capacitors store charge and electrical energy, with capacitance depending on geometry and dielectric material, not simply on the amount of charge present.
Practise Electrostatics
831 free Electrostatics MCQs from Physics, each with the correct answer and an explanation. Unlimited attempts, no account needed.
Discussion
Stuck on an option, or know a faster way to get there? Ask or explain it here.
No comments yet. Be the first to explain this one.
Exams that ask Physics questions like this
Physics is on 16 papers prepared for on TestUstad, and all of them draw the same bank, so this question is worth knowing for every one of them.
More Electrostatics questions
The formula for electric field strength is 'E = F/Q', where E is electric field strength and F is force and Q is the charge. Which one of the following options gives the correct base units for electric field strength?
Two capacitors C1=3µF and C2=6µF are in series across a 90 volts D.C. supply. The total capacitance is given by:
The question is given below:
Consider the charge configuration of a spherical Gaussian surface as shown in the figure. When calculating the flux of the electric field over the spherical surface, the electric field will be due to:
Two bodies are charged by rubbing one against the other. During the process, one becomes positively charged while the other becomes negatively charged. Then:
A neutron, a proton, and an electron are placed in a uniform electric field.