## 2017_1 TMA Solutions - PHY102, Electricity, Magnetism and Modern Physics

Use past TMAs to deal with new TMAs and Exams
Jed
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### 2017_1 TMA Solutions - PHY102, Electricity, Magnetism and Modern Physics

Email: Solutions2tma@gmail.com
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1 The term 'lost volts' refers to -----------

energy per coulomb dissipated in the internal resistance of the source of emf

2 A uniform electric field of 200 N/C is in the x-direction. A point charge of $$3\mu{C}$$ is released from rest at the origin. What is the kinetic energy of the charge when it is at x = 4 m?

$$2.4\times10^{-2}J$$

3 A positively charged object repels

positively charged object

4 The electric potential difference between two points A and B is 42 V. What is the work done by an external agent in carrying a charge of 5.0$\times10^{-5}$ C from A to B at constant speed?

$$2.1\times10^{-3} J$$

5 1 volt is equal to

$$1 J/C$$

6 Which of the following is not true about the electric field intensity $\vec{E}$ of a uniformly charged solid sphere?

$$\vec {E}$$ decreases as a square of the distance from the centre of the sphere.

7 From Gauss’ law which of the following is NOT correct?

The electric flux through a Gaussian surface is a vector product of the electric field and a unit vector perpendicular to and outward from the surface

8 Charges of + 2 C and -2 C are situated at points P and Q respectively which are at a distance apart. A point X is mid-way between P and Q. Which of the following correctly describes the electric field and the electric potential at point X?

electric field is toward Q, electric potential is zero

9 Which of the following is a conductor

copper

10 Calculate the electric field at distance of 320 cm from an infinitely long wire carrying a charge per unit length 8.3 C/m.

$$4.66\times10^{10} N/C$$

11 Two identical balls balls P and Q, each of mass 0.20 g, carry identical charges and are suspended by two threads of equal length. The balls position themselves at equilibrium such that the angle between the threads is 60_{o}.If the distance between the the balls is 0.5m, find
the charge on each of them. Take g = 9.8 m/s^{2}

$$1.8\times10^-{7} C$$

12 Which of the following can be used to charge a metal rod that si held in your hand? Rub it with

It cannot be doe

13 What are the dimensions of the constant k in Coulomb’s law of electrostatics?

$$ML^{3}T^{-4}A^{-2}$$

14 The following are true about electric field lines except that they are drawn such that the magnitude of the field is proportional to the n umber of lines crossing a unit area perpendicular

are discontinuous and may t erminate in a vacuum

15 A tiny ball of mass 0.60 g is suspended from a rigid support with a piece of thread in a horizontal electric field of intensity 700 N/C. The ball is in equilibrium when the thread is inclined at an angle of$$20_{0}$$to the vertical. What are the magnitude and sign of the charge on the ball? Take $$g = 9.8m/s^{2}$$

$${-}3.1\times10^{-6}C$$

16 Which of the following is not true of an electrostatic force?

it is weaker than the gravitational at traction between the charged particles.

17 A huge spark due to electric discharge in the atmosphere produces all of the following except

18 Three point charges $$2\mu C, -4\mu C$$, and $6\mu{C}$ are held at the corners of an equilateral triangle with sides equal to 3cm.What is the resultant force in newtons on the $2\mu{C}$ charge?

$${-}80\vec{i}+69.3\vec{j}$$

19 Two charges $$Q_{1} = 500\mu{C}$$ and $$Q_{2} = 100\mu{C}$$ are located on the XY plane at the positions $$r_{1} = 3\vec{j} m$$ and $$r_{2} = 4\vec{i} m$$. Find the force exerted on the $Q_{2}$

$$14.4\vec{i} – 10.8\vec{j} N$$

20 When amber is rubbed with fur

amber is negatively charged while fur is positively charged

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Jed
Posts: 993
Joined: Tue Oct 10, 2017 6:37 pm
Contact:

### Re: 2017_1 TMA Solutions - PHY102, Electricity, Magnetism and Modern Physics

Email: Solutions2tma@gmail.com
Whatsapp: 08155572788

1 What is the self - inductance of an air-core solenoid, 1m long and 0.05m in diameter, if it has 1400 turns?

4.84mH

2 A single turn coil of cross-sectional area $$7.2cm^2$$ is in the a magnetic field of flux desity 0.45T. The field which is perpendicular to the coil, is steadily reduced to 0.0T in 5s. Calculate the induced emf.

$$0.65\mu V$$

3 The magnetic flux through each loop of a 35-loop coil is given by $$(3.6t-0.71t^{3})\times10^{-2}Tm^{2}$$, where the time is in seconds.
Determine the induced emf at t=5.0s.

17.49V

4 An ammeter is suspected of giving inaccurate readings. In order to confirm the readings, the ammeter is connected to a silver votltameter in series and a steady current is passed for one hour. The ammeter reads 0.56A and 2.0124g of silver is deposited. What is the error is the

0.06A

5 For how long must a steady current of 2A flow through a copper voltameter to deposit $10^{-3}$kg of copper? Z for coper is 0.000329g/C

25.3min

6 A positive ion passes through an electric and magnetic fields which are mutually perpendicular. The electric field strength is 20.0kV/m while the magnetic flux density is 0.40T. At what speed will the ion pass through undeflected?

$$5.0\times10^{4} m/s$$

7 An electron enters a uniform magnetic field 0.20 T at an angle of $30^{o}$ the field. Determine the pitch of the helical path assuming its speed is $3\times10^{7}$ m/s

46.5 m

8 A proton is accelerated through a potential difference of 100V and the enters a region in which it is moving perpendicular to a magnetic field of flux density 0.20 T. Find the radius of the circular path in which it will travel.

0.7 km

9 An electric field of 50 kV/m is perpendicular to a magnetic field 0.25 T. What is the velocity of a charge whose initial of motion is perpendicular to both fields and which passes through the fields undeflected?

$$2\times10^{5} m/s$$

10 A rectangular coil of dimensions 20 cm by 15 cm lies with its plane parallel to a magnetic field of $0.5 W/$m^{2}$. The coil, carrying a current of 10 A experiences a torque of 4.5 Nm in the field. How many loops has the coil? 30 11 If the steady current in a wire is coming directly toward you, the magnetic field lines circle the wire in the counterclockwise d irection 12 A magnetic field does not exert a force on a stationa ry charge 13 A conductor 2cm long carrying a current of 8A lies at right angles to a magnetic field of which the flux density is 1.0T. Calculate the force exerted on the conductor 0.16N 14 In the space surrounding a wire carrying a steady current, there exists a magnetic field circling the wire 15 A series circuit consisting of an uncharged $$42\mu F$$ capacitor and $$10 M\Omega$$ resistor is connected to 100V power source. What are the current in the circuit and the charge on the capacitor after one time constant? $$3.7\mu A$$ and $$126\mu C$$ 16 Kirchhof's loop rule is statement of conservation of ----------- energy 17 A galvanometer of resistance $$120\Omega$$ a full scale deflection with a current of 0.0005A. How would you convert it to an ammeter that reads a maximum current of 5A? connect $$0.012\Omega$$ in parallel to it 18 Kirchhof's junction rule is statement of conservation of ----------- charge 19 Find the current in through the $$0.3\Omega$$ in the circuit shown 0.69A 20 In the circuit shown, each of the cells has an emf of 2V and internal resistance of $$0.1\Omega$$. Find the current in through the$0.5\Omega

3.45A

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Jed
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### Re: 2017_1 TMA Solutions - PHY102, Electricity, Magnetism and Modern Physics

Email: Solutions2tma@gmail.com
Whatsapp: 08155572788

1 The electric field due to a distribution of charges, according to the _________________________ principle, is the vector sum of the fields
of the individual charges making up the distribution

distributive

2 In the relation $k=\frac{1}{4\pi\epsilon_{o}}$, $\epsilon_{o}$ is the ___________________ of free space

permittivity

3 If $$Q_{1}$$ and $$Q_{2}$$ are the magnitude of two charges and r the distance between them, ________________'s law states that the electric force exerted by one charge on the other F is $$F=k\frac{Q_{1}Q_{2} }{r^{2}}$$, where k is a constant

Coulomb

4 The law of _____________________ of charge states that the total electric charge in an isolated system, that is, the algebraic sum of the positive and negative charge present at any time, does not change

conservation

5 A ______________________ is the amount of charge that flow through a cross-section of a wire in one second if there is a steady current
of one ampere (I A) in the wire

coulomb

6 Objects with net unlike charges ____________________ each other

attract

7 Two ebonite rods rubbed with fur and suspended from a rigid support close to each other by threads will ____________________ each

repel

8 There are _____________ types of elctric charges

two

9 ______________________ forces, hold electrons to nuclei, atoms and molecules together to give rise to bulk matter

electrostatic

10 The force exerted by charged particles on each other when they are at rest in a frame of reference is called __________________ force

electrostatic

11 A potentiometer wire of length 100cm has a resistance of 10$\Omega$. It is connected in series to to a resistance R and a cell of emf 2V and negligible internal resistance. A source of emf of 10mV is balanced by a length of 40cm of the potentiometer wire. What is the value of
the resistance R?

790$\Omega$

12 The half-life of a certain radioactive isotope is 32 hours. What fraction of the sample would remain after 16 huors?

0.71

13 A spectral line is emitted when an atom undergoes transition between two levels with a difference in energy of 2.4eV. What is the wavelength of the line?

518nm

14 When a copper surface is illuminated by radiation of wavelength 2537 angstrome units the value of the stopping potential is found to be 0.24volts. Calculate the work function of copper.

7.46eV

15 The work function of a metal is 3.45eV. Calculate th maximum wavelength of a photon that can eject photelectrons from the metal

$3.4\times10^{-7}$m

16 An RLC circuit is used to tune a radio set to receive NOUN RADIO broadcasting at 105.9MHz in the FM band. The resistance and the inductance of the circuit of the radio set are $12\Omega$ and 1.4$\mu$H respectively. What capacitance should the circuit have?

1.64pF

17 An RLC circiut contains an ac voltage source with rms value of 50V and has a frequency of 600Hz. Suppose that a resistance R = 20 $\Omega$, capacitance C = 10.0 $\mu$F and an inductance L = 4.0mH are connected in series to the source. Find the current in the circuit
and the voltmeter reading across the inductor.

2.17A and 32.8V

18 An ac circuit consists of a voltage source $v = 200sin120\pi{t}$ and a $6\mu$F capacitor in series. Calculate the current established in
the circuit

0.32A

19 A voltmeter connected across a 60Hz ac source reads 240V. Write down the expression of the instanteneous voltage as a function of time.

339.4sin377t

20 An air-cored transformer is assumed to be 100% efficient. The ratio of the secondary turns to the primary turns is 1:20. A 240V ac supply is connected to the primary coil and a $6\Omega$ load is connected to the secondary coil. what is the current in the primary coil?

0.10A

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Jed
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Joined: Tue Oct 10, 2017 6:37 pm
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### Re: 2017_1 TMA Solutions - PHY102, Electricity, Magnetism and Modern Physics

Email: Solutions2tma@gmail.com
Whatsapp: 08155572788

1 The $\frac{1}{2} CV^{2}$ =\fracc{1}{2}\frac{Q^{2}}{C}$represents the ________________ stored in a capacitor energy 2 Lenz’s law is an expression of the principle of conservation of _________________ energy 3 Inserting an dielectric between the plates of a capacitor _____________________ its capacitance increases 4 The unit of the quantity, $$½ CV^{2}$$, is ________________ joule 5 The maximum electric field a material can withstand without the occurrence of breakdown is called ______________________ dielectric strength 6 Two 2-$\mu{F}$capacitors in series are in parallel with a 1-$\mu{F}$. The equivalent capacitance of the capacitors is ________________$\mu{F}$2 7 The quantity $$\frac{1}{2}\epsilon_{o}E^{2}$$ represents the electric __________________ energy density 8 In the equation C = Q/V, where the symbols have their usual meaning, the unit of C is called ____________ farad 9 A pair of equal and opposite charges,$\pm{q}$, separated by a vector distance$\vec\{a}\$ is called an electric ____________________ called

dipole

10 If E is the field strength (assumed uniform) and V is the p.d. between two parallel plates which are at a distance d apart, then If E is the field strength (assumed uniform) and V is the p.d. between the plates which are at a distance d apart, then V=____________________

$$Ed$$

11 An electrical insulator is also knoqn as a _________________________

dielectric

12 The negative gradient of an electric potential equals ___________

electric field

13 The gradient of a scalar potential is a _____________________ quantity

vector

14 The work done by an external agent to move a test-charge from place to place in a direction perpendicular to the field is

zero

15 If the work per unit charge to bring a unit positive test-charge from infinity to any point on a surface is constant, then the surface may be referred to as __________________ surface

Equipotential

16 The unit 'joule per coulomb $$(JC^{-1})$$ is also called the _______________

volt

17 The _____________________ at a point in an electric field can be defined as the work done per unit charge moving from infinity to the point

el ectric potential

18 The relation $$\int\vec{E}\cdot{d}\vec{S}=\frac{\rho}{\epsilon_{o}}$$, where S is the surface area and the other symbols have their usual meaning is an expression of ______________' law

Gauss

19 The flux of elctric field through any cross-sectional area is maximum when the angle between the perpendicular to the surface and the direction of the field is ______________________

zero

20 The _________________ at a point in space is defined as the electric force exerted on a test charge placed at that point

electric field

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