# 1991 - WAEC Physics Past Questions and Answers - page 5

41

Two objects of masses 80kg and 50kg are separated by a distance of 0.2m. If the gravitational constant is 6.6 x 10

^{-11}Nm kg, calculate the gravitational attraction between them.A

4.9 x 10

^{-9}NB

1.3 x 10

^{-6}NC

6.6 x 10

^{-8}ND

6.6 x 10

^{-6}N**correct option:**d

F = \(\frac{Gm_1m_2}{r^2} = \frac{6.6 \times 10^{-11} \times 80 \times 50}{0.2 \times 0.2}\)

= 6.6 x 10

Users' Answers & Comments= 6.6 x 10

^{-6}N42

Two capacitors C

_{1}and C_{2}are connected as shown in the diagram. The capacitance C_{2}is twice C_{1}when the key is opened the energy stored up in C_{1}is W. If the key is later closed and the system is allowed to attain electrical equilibrium, the total energy stored in the system will beA

\(\frac{1}{2}\)W

B

\(\frac{2}{3}\)W

C

W

D

2w

**correct option:**e

E = \(\frac{1}{2} Cr^2 = \frac{1}{2}(C-1 + C_2)V^2 = (3C_1)V^2\)

= 3(\(\frac{1}{2}C_1v^2\)) = 3W

Users' Answers & Comments= 3(\(\frac{1}{2}C_1v^2\)) = 3W

43

In which of the points labelled A, B, C, D and E on the conductor shown would electric charge tend to concentrate most?

A

A

B

B

C

C

D

D

**correct option:**e

44

Which of the following is stored by dry Leclanche cell?

A

chemical energy

B

nuclear energy

C

solar energy

D

heat energy

**correct option:**a

The energy stored in the dry Leclanche cell is the chemical energy. It converts the chemical energy to electrical energy.

45

Using the data in the circuit illustrated above, calculate the value of R

A

0.02\(\Omega\)

B

0.05\(\Omega\)

C

5.00\(\Omega\)

D

20.00\(\Omega\)

**correct option:**e

R = \(\frac{V}{T} = \frac{2v}{40 \times 10^{-3}}\)

= 50.00\(\Omega\)

Users' Answers & Comments= 50.00\(\Omega\)

46

A 90W immersion heater is used to supply energy for 5 minutes. The energy supplied is used to completely melt 160g of a solid at its melting point. Calculate the specific latent heat of the solid.

A

2.81jg

^{-1}B

6.25Jg

^{-1}C

8.89Jg

^{-1}D

168.75Jg

^{-1}**correct option:**d

pt = ml 80

90 x 5 x 60 = 160 x L

L = \(\frac{27000}{160}\)

= 168.75Jg

= 168.75

Users' Answers & Comments90 x 5 x 60 = 160 x L

L = \(\frac{27000}{160}\)

= 168.75Jg

^{-1}= 168.75

47

In the circuit above R is a resistor whose resistance increases with increases with increase in temperature L

_{1}and L_{2}are identical lamps. If the temperature of R increasesA

L

_{1}becomes brighter and L_{2}becomes dimmerB

L

_{1}becomes brighter and L_{2}does not changeC

L

_{2}becomes dimmer and L_{1}does not changeD

L

_{1}becomes dimmer and L_{2}does not change**correct option:**a

48

A house is supplied with a 240V a.c mains. To operate a door bell rated at 8v, a transformer is used if the number of turns in the primary coil of the transformer is 900. calculate the number of turns in the secondary coil of the transformer

A

30

B

240

C

248

D

450

49

The diagram above shows a current carrying wire between the poles of a magnet. In which direction would the wire tend to move?

A

into the paper

B

out of the paper

C

towargs the north pole of the magnet

D

towards the south pole of the magnet

**correct option:**b

50

An induction coil is generally used to

A

rectify an alternating current

B

produce a large input voltage

C

smoothen a pulsating direct current

D

modulate an incoming signal

**correct option:**e