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JAMB UTME - Physics - 1990

Question 1 Report

The photocell works on the principle of the

voltaic cell

emision of electrons by incident radiation

emision of protons by incident electrons

photographic plate

Answer Details

The photocell is a device that converts light energy into electrical energy. It works on the principle of the emission of electrons by incident radiation. When light falls on the surface of a photocell, it knocks electrons out of the surface of the material. These electrons can be collected as a current if the photocell is connected to an external circuit. The current generated by the photocell can be used for various applications, including light sensors, solar panels, and even in some medical devices. The other options, such as voltaic cell, emission of protons by incident electrons, and photographic plate, are not directly related to the operation of a photocell.

Read lesson note on Electrostatics (JAMB)

Electrostatics

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Question 5 Report

In a resonance tube experiment, the effective length of the air column for the first resonance is 20cm when set into vibration by a tuning fork of frequency 480Hz. Neglecting and effect, the velocity of sound in air is

96ms-1

255ms-1

340ms-1

384ms-1

Answer Details

λ

= 4(L + C) ; where C = o

$λ$ = 4 x 20 = 80cm

V = $λ$ F

= 80 x 10-2 x 480 = 384ms-1

Read lesson note on Measurements And Units (JAMB)

Measurements And Units

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Question 6 Report

Which of the following is most suitable for protecting the circuit of 2000W electric iron connected to a 250V mains?

13A

8A

5A

3A

Answer Details

P = IV

\Rightarrow

I =

\frac{2000}{250}

= 8A

View Answer

Question 25 Report

When a known standard resistor of \(2\,\Omega\) is connected to the 0.0cm end of a meter bridge, the balance point is found to be at 55.0cm. What is the value of the unknown resistor?

1.10

Ω

1.64Ω

2.44

Ω

27.50

Ω

Answer Details

\frac{R_{1}}{R_{2}}

=

\frac{L_{1}}{R_{2}}

$\frac{2}{R_{2}}$ = $\frac{55}{45}$

R =1.64 $Ω$

View Answer

Question 28 Report

A 0 - 10mA galvanometer with a coil resistance of \(30\Omega\) can be converted to a 0 - 10A ammeter by using

0.03

Ω

series resistor

0.03

Ω

shunt resistor

9.99

Ω

shunt resistor

9.99

Ω

series resistor

Answer Details

To convert the galvanometer into an ammeter, a shunt resistor needs to be connected in parallel with the galvanometer. This allows only a fraction of the current to pass through the galvanometer, while the rest of the current flows through the shunt resistor. Using Ohm's Law, the resistance of the shunt resistor can be calculated. The formula for the shunt resistance is: Rs = G * Rg / (Imax - G) where Rs is the shunt resistance, Rg is the coil resistance of the galvanometer, Imax is the maximum current that the ammeter can measure (in this case, 10A), and G is the sensitivity of the galvanometer (in this case, 10mA). Substituting the values given in the question, we get: Rs = 0.01 * 30 / (10 - 0.01) = 0.03 Ω Therefore, the correct answer is a 0.03Ω shunt resistor.

Read lesson note on Capacitors (JAMB)

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Question 32 Report

A bar of initial length \(l_0\) is heated through a temperature change \(\Delta t\) to a new length \(I\). The linear expansivity, a, of the bar is

$\frac{/ - /_{o}}{/_{o} Δ t}$

\frac{/ - /_{o}}{/_{o} Δ t}

/o(1 +

Δ

t)

/−/o

/(1+Δt)

Answer Details

L−Lo

LoΔt

Read lesson note on Temperature And Its Measurement (JAMB)

Temperature And Its Measurement

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Question 39 Report

To keep a vehicle moving at a constant speed v, requires power P, from the engine. The force provided by the engine is

\frac{p}{v}

\frac{1}{2}

v

pv

\frac{p}{v^{2}}

v

Answer Details

The force provided by the engine is given by the formula P/v. This means that the force is directly proportional to the power provided by the engine, and inversely proportional to the velocity of the vehicle. In simpler terms, if the engine provides more power, the force will increase, and if the velocity of the vehicle increases, the force will decrease. So, to keep a vehicle moving at a constant speed v, the engine needs to provide a force equal to P/v.

Read lesson note on Heat Energy (WAEC)

Read lesson note on Work, Energy And Power (WAEC)

Heat Energy

Work, Energy And Power

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